I also switched from a Dell to a Macbook Pro, and I have to say everyday life wise it was the best decision I ever made. However, most of what I do is film editing and digital art, which Macs seem to be geared towards. I don't game on a regular basis, and Sims 3 is the only game I play. (No WoW, etc.) I've played Sims 3 on my Macbook for extended periods of time, generally on roadtrips, and it drains the battery pretty fast. However, I've found that using NRaas No Intro and No CD have stopped my machine from overheating when running the Sims 3. I currently have LN & Ambitions installed with no stuff packs.

Here are my specs:

I am on a 13" Macbook Pro running OS X 10.6.6 with a 500 GB HD
  Processor Name:   Intel Core 2 Duo
  Processor Speed:   2.4 GHz
  Memory:   4 GB
  Chipset Model:   NVIDIA GeForce 320M

Hope that helps you out. Happy gaming. --Roo
edit: I forgot to mention, I don't run my game graphics on high. It drains the battery and heats my system up pretty quickly. Medium works just fine though. Also be aware that programming can kind of be a pain in the ass on OS X.