I've experienced lagging issues too, but they've actually been very few and far between, and when they do happen, usually clicking refresh a couple of times fixes it. One thing I have been having problems with for about a year or so is the occasional choppy playback; I'm not talking about how bad it was years ago when I had my old computer that was barely puttering along on 512MB of RAM as opposed to the 8GB I have now, but like sometimes it looks as if the video playback just isn't as smooth as it could/should be.
And while we're on the subject of playback, does anybody know how to set your videos to play in 480 or higher by default? I see some vids out there that do, and I remember once hearing about a certain tag you type or a certain code to add in the description box that supposedly does that, but I remember trying it and my stuff still played at 360 by default.