Usability Yes. Social Features, Uh-Oh.
Some of the scepticism surrounding social features centres on the idea that it will enable people to set up cabals. I feel that provided our policies remain in place we have the means to identify and combat those. I would reject any social features that allow people to form groups and discuss things in private (such as "let's all go vote 'oppose' in this poll"). All activity should generate a history/contribution log that can be examined by everybody.
Anything that makes collaboration more efficient will be open to abuse. My position is that we have to support the good faith user and just accept that anything positive we do will have some negative consequences. Examples:
WYSIWYG editing will make it easier for vandals to disrupt templates in less obvious ways than merely breaking them.
Easier upload of pictures will make it easier for users to upload a picture some might judge obscene.
Nevertheless I would see both innovations as net gains. I think social features as currently outlined in the recommendation will be a net win, with the instances of abuse being outweighed by the advantage of attracting new users and making WP a more appealing place to spend one's time on the internet.
Whilst I have sympathy with the view that people spend too much time on their user pages, I actually see that some of our most trusted and valuable users have indeed gone to a great deal of effort to make their user page very attractive (though they also tend to make them more useful to themselves by adding shortcuts to oft-visited pages). I've spent quite a lot of time on my own en:wp user page and I like sometimes to revisit it as it's like a record or history of my time spent at Wikipedia. Sometimes it's almost like a friendly face to return to when you feel a little alone in the community. In short, it's more desirable someone spend an hour moving toward a featured article than fiddle with their own domain, yet it's a pretty harmless activity and keeps the person in touch with their account, which is better than the person not being on-wiki at all since such a person may drift away for good.
When I get interested in a new topic I quite like to visit the page of a user who has contributed heavily to that topic and I'm somewhat disappointed if I don't find out at least a little about that person from their page.