Thanks to all of you who wrote to us telling us the site was running more slowly than expected. We're happy to say that last Friday night our engineers rolled out a profound set of changes to our database architecture. YouTube's growth has been breathtaking (thanks to you!), and our infrastructure has had to grow very quickly to keep pace.
These changes were in the works for quite a while and they represent a lot of hard work by a dedicated team. What happened was that millions and millions of accounts and videos were migrated one by one to new database clusters while the site was up and running. It takes a huge amount of time to perform this kind of operation -- you can think of it as the equivalent of changing the motor in your car while you are actually driving on the highway.
With these changes in place, you should see all manner of improvements, including speedier comment and profile updating. We've also just added extra machines to process videos much more quickly, so that should be noticeable too.
The YouTube Team