I kind of had the same feelings when I got my iMac. I didn't have Internet for a month either - what is there to do? This is general new-Mac stuff, not iBook stuff. No battery advice from me.
Get all your important data moved over. You can always get stuff you forget later, just don't throw away your PC (or old Mac). If you have an old Mac, set up firewire target disk mode to completely copy your old computer over.
Set up your accounts. People are generally advised not to use your admin account for web surfing, email checking, etc. I also set up a guest account, so if someone else wanted to use the compy, they could without screwing up my account.
Freeware! Let me think - at first, I downloaded disk image files (.dmg) on my PC and moved it upstairs with a flash drive.
Quicksilver has been very invaluable to me - it is said that no Mac is complete without it.
Firefox is necessary - Safari is by no means perfect, and I love tabbed browsing. Netnewswire Lite is a nice free RSS newsreader, but I'm sure there are plenty out there.
AdiumX is a great chat client. It supports AIM, MSN, Yahoo, ICQ, and many other chat servers. Its very customizable and extremely attractive. Growl (I don't have a link) is a great systemwide notification system. Gmailstatus is a cool menu bar tool to see how many emails are in your gmail account.
Get your peripherals hooked up - external mouse, scanner, camera, iPod, etc. If you find you need a USB hub, get that before you run out of ports. Burn all your CDs to iTunes (if you have Internet access). And you're set.
These are the kinds of things I did. Enjoy your new Mac!
Calih