Since you're switching from Win, there are probably a few utils you might need to tide you over...
I switched two months ago, and these were the ones I found useful. Of course I've been using RH for the past three yrs, so that tempers my requirements.
1) SideTrack - to put a scroll-wheel, right-click, click on tap etc, onto the trackpad.
Essential!
2) MPlayerOSX - cos Quicktime doesn't do full-screen(idiocy IMO) and you need to play DivX etc. VLC is also a good option.
3) iTerm - if you are a terminal kinda guy - allows multiple tabbed terminals.
4) OpenOffice, if you need a word replacement.
5) DVDibbler - to rip and backup your DVD collection.
6) ffmpegOSX - to do a lot of neat stuff with video.
7) fink is essential if you want to try out the myriad programs ported from *nix.
8) I use thunderbird, as I check mail from multiple places, and Mail refuses to show things that are marked 'deleted' on my IMAP inbox (any suggestions?)
[Edit] - I'm using PandoCalendar - it is a pop-up calendar when my mouse goes to a corner. I'm used to having a calendar when I click on the time in RH, and this is something I missed very badly in OS X.
All the above are either open source, freeware or shareware.
Have fun!!
