It would be cool to have a way to switch "natures" of your Mac OS X, not unlike the way I change Perspectives in Eclipse from PyDev to Java whenever I start hacking different project. Let me illustrate it on one simple example. When I'm at work I'd love to have my work resources connected and available in Finder. That includes, say, some network shares, VNC servers, and so on. And — I would like to have them just in Finder's "Places" menu. When I go to uni, I'd love to have my Birkbeck folder there — may be not only this folder, but some of it's subfolders too, so I shouldn't go to Dropbox/Birkbeck/IBIP/Lectures just to find my image-based information processing lectures, I would rather select IBIP shortcut in Finder and get straight to it. But there's a problem — I don't need my IBIP shortcut at work. More than that, it would probably distract me and this is the last thing I want. On the other hand, my work network shares would be more than pointless at uni, as they'd be not only useless but even inaccessible without a VPN (and why do I need a VPN at uni?).
So, you see, Mac is good and Mac is cool, but quite a few things could be improved. (however, maybe I should spend a little bit of my time and write a script to fix all this stuff for me? that would certainly work...)