I have three, one office-issued, one I use for work and one I use for personal. The office-issued model sits in a desk drawer. My work MBP: Thunderbird Firebiird, VNC, Notes, Calendar, Growly Notes. My personal computer: Think or Swim (heavyweight pro trading platform), Fidelity Active Trader Pro (another heavyweight pro trading platform), Firefox, Apple Mail, Notes, Calendar. Sometimes I run emacs on all of the systems. Sometimes terminal window. Sometimes TexMaker and lots of other programs for various types of work.
The biggest things that I run are the Trading platforms and I'd like to move up to 32 GB of RAM in a machine so that I don't need three machines.