I used an Ubuntu certified desktop (well, laptop) and things did not just work (TM). It generally failed to recognise my second monitor unless I opened the system settings, then closed it. It also failed to recover from sleep on a regular basis and got terrible battery life. Needless to say, I ditched Ubuntu. I think it's junk, to be quite honest.

I'm using Crunchbang on that laptop now and it's mostly better.