I know Unity is universally hated, but I am fond of its keyboard support. I rarely have to use my mouse and I using keyboard instead of trackpad in those situations saves my time.
I don't use all the gestures, just a few of them. But I've been doing it for so long they're second nature to me.
Two finger scroll one of the most important. I remember trying to use friend's PCs before it became common and being frustrated every time.
Two finger click works like a right-click, so I don't need to hold a key or dedicate part of my touchpad to right-clicking.
Three finger swipe left/right is amazing. It functions as a forward/backward gesture. In Safari it moves through history. In IntelliJ (my IDE of choice) it does the same thing, which is invaluable. I don't even know the keyboard shortcut in IntelliJ, it just works. And it works in Chrome. And Xcode. Having a universal gesture is fantastic.
Another favorite is four fingers up, which activates Expose. When you're moving between multiple applications and copying & pasting it makes makes things so much easier. I don't have to move my hand off command-C/V.
Four finger spread shows the desktop, which I use occasionally.
Double-tap with two fingers zooms in iOS style in Safari, which can e useful
Double-tap with three fingers opens the dictionary (& Wikipedia!) anywhere in the os on whatever you tap on. Reading an article and don't know what something is? Just double-tap three fingers and a little pop-up tells you. It's one of those functions that's always been there but it's so easy to get to I actually use it now.
That's what I use. There are a few more. Four fingers together opens Launcher. In Safari the zoom out gesture (pinch two fingers) brings up a tab-list, but I keep forgetting that's there since it's a relatively recent add. Four fingers down is Expose for one application, but I don't have much need for that. Two fingers from the right edge opens the notifications in Mountain Lion (which I don't really use).
If you're a multi-desktop person, four fingers left or right switches between desktops (including Dashboard) and every full screen application. This also works for app switching on iPad 2/3/4s.
Really it's like using command-c/v to copy and paste or command-tab to switch applications. It's quick and easy to do, and you quickly forget it's there and start doing it automatically.
Honestly I hate helping coworkers with a problem in IntellJ because they all use normal mice and I can't easily jump back to the last place I did an edit (even in another file). I'm working on helping them and then all of a sudden there is a brain stall while I realize that I can't just do a swipe and have to think to go click on the tab I want.
I feel handicapped without them; like something is missing. I remember how much I liked getting a button on the side of my MS IntelliMouse I could use to go back when surfing, this is like 100x that.
Edit: It just occurred to me that these aren't default gestures. A few of them changed in Mountain Lion and I set my Macs back to the way Lion had them, so you may have to experiment.
two finger scroll and two finger right click is almost universal now. When inside a browser, I rarely use the mouse scroll and prefer to use spacebar or up/down keys to scroll for granularity and I know where each action is going to land me (spacebar = page down, up/down key = just one line)
For forward/back I use Alt + right/left arrow. This works in browser, file browser, Eclipse. I suppose this would work in IntelliJ as well. In Eclipse, This doesn't take to the last place you made edit at, but the last place you had focused at (across files). Besides there is a shortcut Ctrl + q to go to the last place of edit (across files) in Eclipse. There are equivalent shortcuts in other editors that I have used.
There is no equivalent of Expose in Ubuntu. But how does it differ from using Alt + tab? When all the windows are exposed do you have to move your mouse pointer to the window you want to focus on and four fingers again? I think that's how I remember it. I love Ubuntu's Alt + tab and Alt + ` to be honest. You can also use left/right arrow keys with these two options. Granted, I do have to take my hand of Ctrl if I am doing copy/paste.
So three finger double click seems to be the only action I see myself to be missing that I would use.
As I programmer, I am typing for most of the time. So honestly, I think keyboard shortcuts work faster as I don't have to move one of my hand everytime. This is specially true if you are working on a desktop as you really have to move your hand to the magic mouse. YMMV though.
One of the things I hated about Mac was there are no equivalent of 'Super' key shortcuts which are present on both Windows and Ubuntu. Like Super + 1 launches the first application in my doc. This is much faster than opening spotlight and launching an application from there using a keyboard. Also, some of the shortcuts are not universal. Chrome used Ctrl + tab to change the tab and Firefox used Cmd + tab (I suppose?). Being from Windows/Ubuntu background, it was really frustrating to get used to the Cmd key at some of the places.
One more mouse gesture related thing I would like to add is that I love FireGestures add-on on Firefox. If I am just reading news/sites and not typing, I use my mouse and FireGestures + mouse works great. Firefox is my primary browser and I didn't find any equally good extension for Chrome.
The nice thing about forward/back gesture is that it works almost everywhere, and I don't have to learn a different keyboard shortcut for each program. I accidentally discovered it worked one day and it stuck. It had never occurred to me to go searching for a keyboard shortcut to do it.
Expose is quite nice. In OS X command-tab switches between open applications (not windows, applications). There is no list displayed like Windows XP had. When you trigger Expose, every open window is automatically arranged on screen. You just click it with your mouse and everything moves back into place with the window you clicked now at the top.
I use command-tab when I'm in keyboard mode (such as coding) and Expose when in mouse mode (surfing, browsing email, etc).
I think you're right bout the Super-1 shortcuts. I don't think there is anything like that in the Mac. I usually have every program I'm using open, but when I need something else I just use Spotlight. Command-space opens it (I believe that was the old key combo, which I set Mountain Lion to use), I type a few letters, and hit enter. There are other programs that are faster or more powerful (Quicksliver and Alfred are popular), but Spotlight was good enough.
Tab switching doesn't seem to be standard. I know that in Safari the key commands are Command-[ or Command-], but I don't know if that works in other programs. When I first switched it didn't take too long to learn when to use command. But I also used Macs when I was a kid, maybe that helped.
One pleasant side-effect of the way the Mac has evolved is that the keyboard shortcuts work perfectly with Terminal. Both control and meta ('option' on the keyboard) work exactly as you expect. Control-c quits programs, control-d sends end-of-line, emacs is easy, etc. But the command key isn't used by any unix program I know of.
That means it's free to make life easy. Copy and paste are still command-c and command-v. You can clear the terminal with command-k, and standard window management things (-h for hide, -tab for program switch, -` for window switch) all work without interfering with whatever program you're running.
It's a total accident of history, but it worked out great.