Awesome! I have an iBook G4 and a dual G5 PowerMac; no Intel for me yet. I love doing video and photo work on the big one, and the laptop is like an oversized PDA. Everything "just works".
Pick up Adium for all your instant messaging needs, Skype if you like, Firefox for Mac for those few websites that don't work with Safari.
If you have Airtunes speakers, then Airfoil is an awesome product (redirect ANY app to your remote speakers), and Audio Hijack Pro will take any audio-producing program and reroute it to anything else (including to file). Bitpim can talk to your cell phone if iSync can't, the built-in screen sharing is just VNC, you can get a Microsoft Remote Desktop client, Flip4Mac to view .wmvs, GPS Babel+ and Google Earth go great together on the Mac, and the list goes on with more things I could recommend. You also want Growl, the integrated notification framework. It's hard to explain, just Google for it.
Welcome to the universe of light!
