Debt.
Lousy attention span.
Those, and a bad hip. Can't win them all though.
For what it's worth, things could be a lot worse for me. I sold off all my computers recently to help with bills, and am now myself using a broken-screen PowerBook G4 as my main computer! When things get a bit better, I may look into a G5 tower, another MacBook Pro, or an aluminum iMac. We'll see.