The MD-90s are indeed on their last legs. I am flying a 737-800 round-trip on the SJC-LAX route next month. The flights I'm taking are both currently operated by MD-90s. Effective April 1st, 737-800s takeover.
There are also some regular AA MD-80s (ie... the polished aluminum exterior panels and standard interior configuration) now operating on the ex-QQ routes.
I loved flying the MD-90s, due to their whisper-quiet noise level up front and impressive takeoff power and climb rate. I'll be sorry to see them go.