Why do so many of the things I've seen on YouTube the sound is slightly out of synch with the pictures?

Possibly connection and file format interacting. Compress video and audio enough to make it (relatively) small, and you lose information. Sync data is almost certainly one of the things they've chucked out, on the grounds that they can (mostly) get away without it and reduce bandwidth and storage. Most streaming video does the same - RealPlayer used to be pretty bad for that too, even doing it for files playing from disk.

Graham.