I have heard some complain about load times.. In all retrospect it does contribute an attribute when rating an OS but hardly a measure of integrity. I also had some trouble with my video driver, but again for my it was just a server, no need for anything fancy.. I must say its damn rock solid, but most linux build are.
I dont think ubuntu is ready to consume the market. But its getting there... Give it 5 years and by then Microsoft will have programmed them selfs in to a shell they cant get out of. That is if they go forward with their plans. I hope for their sake they think it over, but who knows.