I use several machines. For capturing/probing/listening, I use a Lenovo Thinkpad X120E, sort of like a buffed up netbook... you really don't need a lot of power to do those as Darren often demonstrates this on his Asus netbook. If you're going to use WPS-based attacks via Reaver, this is more than enough for that purpose.
I also use a 2011 Macbook Pro for exploring/learning different tools with all of my pen software running in a VM (parallels) which I firmly believe is superior (and easier to use) than VMWare Fusion. You could say that this is my educational/experiment machine. However for decrypting/bruteforcing/wordlist/rainbow hash attacks, I use a mini-ATX box with a real GPU. So the idea is to capture the information you need on the Thinkpad/Macbook, export it to a usb flash drive, reimport it and process on the more powerful machine (mini-ATX box). My Thinkpad processes about 300 keys per second, the Macbook about 1800-1900 kps, the mini-ATX about 42,000 kps.
The key thing here is no matter how powerful your laptop is, I don't believe you can get any GPU acceleration working if you run, say Backtrack/Kali in a VM because your video adapter gets assigned a virtual adapter driver (i.e. VMware SVGA), so you'll want to run it native or as a Live OS if you want that GPU acceleration.