YouTube is experimenting with a new personalized homepage. Currently in limited beta, these homepages are available to a random group of Youtube users. If you want to check out how this new homepage looks like you can access from here, remember to login before accessing this page.
The new homepage will show personalized recommendations based on user interests along with regular Most popular and featured videos. The personalized recommendations are based on videos your viewed earlier and the videos you added as favorites. Another feature is that it shows new videos from your subscriptions along side.
Friend activity is another new feature that will show your friends activity on Youtube. It is not yet clear when these features will be available to all users.