@dentaku: I've had buffering problems lately, but only at 1080p.
What has annoyed me about Youtube for years now is that thing it occasionally does where it just stops loading at some random point, and the only way to get past that is to drag the scrubber a couple of seconds past that point, or completely refresh the page. I can't believe it still does that.
At least YouTube's scrubber gives you a live video preview. Having an inactive scrubber was permissible back in the mid-1990s when Media Player was introduced, but it's 2011 now, and Media Player in Windows 7 still doesn't have an active scrubber, even though DirectShow and Media Foundation both support it.
Why Microsoft, why?!