I got to 40 apps (and 41 "windows" since one of the apps was the browser which displays two windows) on the stock 600Mhz kernel, including some "heavy" programs like Open Office, Super Tux, and Angry Birds. Task switching was getting sluggish and was just usable, until I opened the 40th app, Tux Racer. That killed the task switcher.

Eventually a window opened allowing me to kill the programs not responding. After a long time (about 30 minutes) it did and everything was back to normal.