ERROR: class 'Qt::Thread' not found
Oh, what's wrong? Paths are correct and there's no typo. I searched about this matter on the web, then found some information on ruby-talk-google.
There's no Qt::Thread because Ruby lacks support for native threads
(at least, for the moment), so it's not really feasible to implement.
Okay, I see. Certainly, Qt's thread is native thread, and Ruby 1.8's thread had been a green thread. So it's no worse that QtRuby wasn't support QThread(Qt::Thread).
But now, Ruby 1.9's thread has become native thread. So this is improvement point for QtRuby.