I have an android build going for gumstix overo if you're interested (it's an older version of android). Though there are probably more recent builds somewhere on the web...
has been a while since I've touched it though - so would likely be pretty rusty to answer many questions
I can tell you that the design is very similar to the beagleboard (OMAP3530, similar memory bus, etc) - just packed in a smaller PCB - and with a few different components. Because of this, you can use a lot of the examples for the BeagleBoard on Gumstix boards
-Steve