Once you go mac, you never go back. The reason I bought macbook 3 years ago because I can install windows on it. During the first month, I was using 30% of the time. Now, I only open them when I want to use the MS Office and it still annoys me to the point I'm considering to buy MS Office for Mac.
As totherail said, you just need to make sure you know what your home folder name should be and not regretting it later. You'll be asked for your wifi password. Update is straightfoward. The installation process will be different than windows. Mostly, you'll just need to drag and drop it to your application folder. Uninstall program, just send them to trash can. Learn to use command + shortcut instead of control + shortcut in windows.
Do consider to buy ipod touch to maximize your mac experience. The address book and ical will work nicely as your personal organizer when you combine them with ipod touch.
Other mac programs I recommend:
insomniax - to keep the mac running even if you close the lid.
caffeine - Keep the display from sleep
Onyx - System maintenance tools
1Password - Keep your internet password.
Btw, OSX lion is coming up soon in summer. If you buy it at Apple store, try to get the free update for osx lion.