I'm running Ubuntu at work and OS X at home. For a workstation Ubuntu is fine, but I'm not going to give up OS X. I develop on both and the experience is similar, but the OS X gui is just what I prefer.
Because of window shading, tabbing together groups of windows, focus on mouse and vastly better terminal support (including Yakuake, a terminal that behaves like the doom console) I am roughly twice as productive on Linux as on OS X.
That is before you add in apt-get, but honestly if I had to put up with Fink on Ubuntu I still wouldn't switch because of the interface limitations.
Could you explain what you mean by tabbing together groups of windows, and focus on mouse? I definitely prefer macports to fink and apt to both.
There is a video of Compiz Group Tab here: http://www.youtube.com/watch?v=1nK4_cH5sbM&feature=relat...
Focus on mouse comes in several flavours, the best seems to be sloppy focus with raise-on-focus disabled. When you mouse over a window it goes active so you can type in it. Because it doesn't come to the front unless you click on it you can leave your IM window/IDE/whatever half under a browser window and still type into it. Truly a killer feature, especially on laptops where space is limited.
The best way to do window focus, tho, is, I think, to have you machine's camera notice where you are looking, and automatically raise that window - iris tracking and window raising.
The Focus on mouse software sounds very cool though. When you first said it I thought you were implying Ubuntu developers had more of a focus on mouse actions which was why I didn't just google it. :)
The advantage over just bringing forward the work sheet you want each time is that as you move one around and resize it (to cater for fitting the source data on the screen), the one you aren't currently working on changes with it saving you some clicks. It sounds like a stupid little thing but taking a frequent minor irritation out of your environment can be surprisingly beneficial.