I was riding this '87 Diamondback Apex for awhile, it was an awesome bike and I probably put 2000-3000 miles on it as a commuter and I did some trail riding on it as well. I finally admitted it was too small so I sold the frame about 6 months ago. I'd really like to find another one with a 20" frame.
I just picked up two vintage mountain bikes this past week, the first one is way too small, the '84 Stumpy has a 17" frame and 24" wheels. I'm not sure why I bought it, other than it was cheap and really cool. The '85 Schwinn High Sierra is too big for me as a trail bike but it will make a great commuter, set up with a rack, road slicks and panniers. Both of these bikes are in the process of being cleaned up/overhauled.
I have a rigid '93 Univega Rover that has been my commuter the past year or so and I've just recently set it up for trail riding and am having a blast with it. The 21" frame fits me really well and many of the Deore components that came off of the above DB Apex have now gone to the Univega, I don't have a picture of it available at the moment but will post one later.