I'm having the same issues.
When hardware accelaration is enabled, i get stuttering, choppy picture. Its not constant, but pretty apperent. Using the latest version (30).
My platform is using Intel Atom Z3735F with Intel HD graphics. I'm using the latest intel drivers.
Disabling accelaration makes the issue go away, but this is not desirable, because CPU on its own isnt all that powerful and quite struggles with higher resolution videos.
Also, HTML5 for some reason doesnt work with youtube.
I tried with firefox and html5 and hardware accelearation work like a charm. But i want to stick with opera.