After using a PC (with DOS, OS/2 and various flavours of Windows) for over 14 years now I'm still amazed at how smooth the switch was. I'm also amazed at how much I now love this Mac. I must have turned into one of those Mac-luvvies now :). I really love it. Its such a great UI that even just surfing the web or writing email seems more fun since it all looks so gorgeous.
I spend alot of my time working with other servers & machines so having really nice X & VNC support is very nice as well. (I can't put my finger on it, but its never quite the same using X on windows).
If anyone else is thinking of switching, I found that CodeTek's Virtual Desktop to be excellent and is the first Mac software I've bought ($30).
Also I found that the easiest way to move all my mail from Outlook Express to the Mac was to use Mozilla on windows to import Outlook Express into mbox format, then import the mbox's into Mac Mail. I like Mac Mail alot too.