Enable Gmail shortcuts, learn them and love to use them. Also, enable the 'gl' shortcut in the Labs page again (gl = go label.). They will make your life a lot easier, and I can't stress this enough. E.g., to go to label 'llvm-dev' and mark everything read, I just type: "glvm-d" (it maches on substrings) and then just "*uI" (select unread, mark read).
For to-dos, I use Gmail's Tasks feature (look for it in Labs settings). Shortcut "gk" goes to it and I can quickly add a to-do.
The idea is, only personal email should ever reach your Inbox. And once it does, I usually Archive it as soon as I'm done tending to it. I'm sure there are more things that I don't consciously think about and are muscle memory by now, but those features I find myself unable to live without.
Also, I was trying to wrangle my email a bit earlier this week, and discovered that going from 50 message on the front list to 25, and eliminating the multiple inboxes feature, really made my mailbox a lot less intimidating.
I delegate on the basis of "Get ... done, by ..." and manage by exception. I discourage cc'd stuff and unsubscribe from everything that is directly relevant. It is a huge trap to appear important because you are across everything. I ration my time and anyone who abuses it by making disproportionate demands via e-mail, IM or phone is 'tutored' and if that fails, cut loose.
What I do:
I personally use Things.app with a dozen or so various "Projects". Each Project in Things is its own areas; a particular class I'm in or something that I'm hacking on.
When something that I need to do for any of these Projects comes up, it goes right into Things. If I'm in class, I'll add it to my iPod and then sync up with my computer later that day. I add an artificial deadline to complete the task, if there isn't a real deadline.
What my roommate does:
My roommmate has another, simpler approach that I like: He just has a giant pad hanging on his door and writes down what he needs to do on there. So he sees it whenever he leaves his room as a reminder.
When he finishes something, it puts a giant X over the item. He doesn't have dates written down, but tries to have everything he has written down finished by the end whatever the time period is when he removed the page.
However, you're not me or my roommate. So, here's some other things to look into: OmniFocus, TheHitList, Anxiety (http://www.anxietyapp.com), TaskPaper (http://www.hogbaysoftware.com/products/taskpaper) and a bunch of other very nicely done apps whos name escapes me at the moment to look into, if you want a program to help you manage things. And of course, theres always non-electronic things (datebook, moleskine/generic notebook, post-its, etc) that you could use if it helps you work.
Plus lots of sensible email filters, of course. (But that's something you gotta figure out for yourself, sadly!)
And one-touch handling really helped me deal with the flood of emails. After I started doing it regularly, I was usually able to clear out my inbox whenever I logged in. But it also helped that most of it was junk and I could immediately trash.
So I read a lot of things on GTD but didn't end up adopting most of them. What I did adopt was their rule that if you can respond to or deal with something in less than X minutes (2? 3? forget the number) then do it immediately.
This made things so much more manageable and has kept my inbox size down tremendously. Before I found that it had filled up with lots of emails that I knew I should respond to or had to do something to follow up on, but just hadn't yet.
Deep down, can't beat a good moleskin these days really.