A colleague forwarded me an email about Elsevier's social bookmarking service. It's eye-candy index is definitely 2.0. I haven't signed up as yet, but have read through this "kinda" review, 2collab: A review, kinda. This was written in late November, it may be that some of the reported bugs have been ironed out by now.
One thing I have noticed is a lack of RSS feeds.
I'll put this on my list of things to investigate.