Okay, it sounds like this is an issue with YouTube's servers -- sometimes, on videos they syndicate, it can take some time to load. I'm currently experiencing the same problem on pages that have YouTube videos, but pages that have videos from other sources, like Google Video, are working fine (
here's an example).
Part of the risk with a mashup site like ActoGuitar -- we're always susceptible to the troubles of others. Hopefully YouTube will have this issue sorted out soon.