In February YouTube began beta-testing its personalized homepages for individual users. Such personalization on YouTube was a long time coming, considering the advancements seen in other social media recommendation services and even third-party recommendation services that pertain directly to YouTube. Based on the feedback received in these past few months of beta-testing, YouTube is now ready to launch the personalized homepages with a few improvements.
The video recommendation system has likely been tweaked, though this hasn't been explicitly stated by YouTube. If it were up to me, I'd say that the tweaks are unnoticeable -- one of my recommendations was for the same video I've already favorited, just a copy that's been uploaded by another user. Our Editor-in-Chief Adam Ostrow, however, had a much improved experience with his YouTube recommendations, which were accurate based on what he'd favorited.
Nevertheless, if repeat content could be minimized in recommendations, that would be a vast improvement for my personal experience (I know it's hard, but eventually doable). The most notable improvement to YouTube's personalization features would be the tweaks made to the email notification system.
Text for comments and messages are included directly in the body of these update emails, so you can see what these messages are without having to return to YouTube and logging in. I haven't received any update emails from YouTube since this particular feature upgrade was rolled out, so I can't say this for certain, but direct reply options for messages and comments via email would save users (especially power users) even more time.