Video quality from online sources is often an issue. Resolution settings can often be adjusted though bandwidth and computer speed still need to be sufficient to keep video from getting too choppy. Hulu uses Flash video, which is ok, but it's a processor hog when you run full screen video. The Flash issue seems unique to Hulu (and Hulu Desktop). YouTube uses Flash too but they don't toss in as many bells and whistles so it seems to be smoother. YouTube has an HD option for some videos, and this often has problems being choppy. Netflix uses Microsoft Silverlight for the video. Each time you connect it decides what quality setting you will receive and adjusts to compensate. As a result I haven't had problems with Netflix stalling or stuttering. This is similar to how Real media can be used.
To resolve the Hulu - Flash problem I made some hardware changes mentioned in the A/V section and then messed with Flash and Firefox. If you right click a Flash file you can change the settings to allow it to store more information on the computer. That helps in primarily when caching (bandwidth) is a problem but it was not effective across the board. One of the few actions suggested making Hulu work better was to take Flash out of the loop. There is a program called VLC that is used to play most every kind of audio and video file. I might be giving it more credit than it deserves but it seems to be a much less When you install it you can check an option to install the 'Mozilla Plugin'. When you do this it will use VLC to run any video that is in Firefox and as a result, bypass Flash. It helps quite a bit though the commercials still lag.
Hulu also has this annoying stutter that it does after resuming from a pause. I can't sort out why it happens exactly but I do know that to resolve it all you have to do is manually track to another spot on the timeline. Simple but tedious at times.