SRAM Force rear derailleur goes boom

I learned something last week: a SRAM Force rear derailleur can only accept cassettes up to 27 teeth.

I learned this because I let someone try my PowerTap wheel and put his wheel on my (brand new) bike. I NEVER thought this would cause my rear derailleur to explode specatularly.

Lesson learned: no more generosity with wheels.

Results: pretty pictures, $117 for a derailleur - thanx to Masherz of Woods cross who were nice enough to meet me 1/2 way on matching an internet price, and $10 for a new derailleur hanger.