Hi,
if anyone has tried to do anything useful with stock (non-Linaro) 4.2, you'll probably have noticed the "Developer options" item in Settings is gone, and adb is disabled by default, with no obvious way to turn it on.

There's a way to get it back though (but it seems to be hidden to anyone who doesn't read the source): Open Settings > About phone (or About tablet), then tap the Build number entry 7 times.
After that, "Developer options" will be back and you can turn on adb.

ttyl
bero