I do do miss windows to be honest (and I still have a windows machine), not because I prefer windows to OS-X, but there's a lot I can't do on my Mac.
1) I use a program called R (a stats package) and whilst the core distribution runs on OS-X there's a number of "library" packages that don't.
2) MS Office isn't native yet
3) There's a good deal of maths applications that don't have universal binaries yet.
4) It can be annoying reading Adobe PDF's in Preview, when I click CTL-DOWN it moves to the same point in the in following page that you where at in the previous page, rather than going to the top of the next page... mighty annoying
5) It's hard to find cheap add-ons for example I wanted to get a USB device that had composite-in, I am yet to find one.
But the good features far outweigh any of the above, in particular:
A) Networking - it is FAR easier to get my Mac to detect my PC, than the other way round. X11 is great for SSH'ing into a server and running a graphical app.
B) The Expose (thats the hot corners thing right?) is outstanding, especially if you have LOADS of windows open like I normally do. You just flick your pointer to a corner and I get a little version of all the windows, and I just click on the one I want, MUCH better than ALT-TAB in windows.
C) Connecting extra monitors is VERY easy, and I encounter no problems. On windows for example if I have a video playing and than transfer it to another monitor, it crashes.
D) I like that you have decent Unix style command line when you need it, so you've got all your data manipulation tools like grep, cut, head etc..on windows you'd need MiniGW /MSyS.
E) There are lots of Mac only academic bits of software, a good example is Papers which for anyone who deals with large numbers of research articles (so hence any postgrad) it's a must.
F) Although I can't play games on my Mac, for me this is quite a good thing, I treat it much more like a work /research machine than my PC (which is quite the opposite of the Mac adds I know).
G) I like the fact that there's not a bizilion different combinations of hardware (so I dont have to read the backs of software packages looking through something like:
AMD 1.4GHz Athlon or Intel Pentium 4 1.4GHz or etc..
512 MB RAM
Geforce 2 or better or ATI radeon 9200 or better Direct X 9 compatible GPU
Direct X 9 compatible 5.1 channel surround sound card or better
etc....)
On most mac software it's just
Intel Mac or PPC 1.4GHz +
In essence once you look past a few annoying bits and peices, a Mac is a far more efficient work tool and more enjoyable operating system to use. Although I've not used Vista yet. And whilst it's not true that Macs "dont crash" (because they do, and quite a bit too, R has crashed my Macbook tons of times) they are much more stable than windows. If software companies get there act together and start porting their software to intel based Mac's I honestly think Apple have a chance of taking a large part of the hardware market in the future, that is if leopard isn't crap!
David