I just finished reading through the final report from our usability team (three college students who agreed to do testing of our game for their class project), whom we're meeting with in about half an hour. They made a number of useful observations and recommendations. I came up with a bunch more ideas reading through their report. There were some tests we wish they'd done, but OTOH it was also free labor. The two big conclusions:
1) We have already implemented most of the fixes they recommend. Go us!
2) Out of the six non-target-demographic playtesters, there was one that really like the game. Let me repeat that: there was a playtester that really liked our game! There was somebody who really got it and understood what it was all about, and he liked it, too.