It is much better than having two clicks (which I had prototyped), but the prob is that a lot of portable devices don't have 'hover' - so I don't know if it falls back on anything in that case.

There is a product here - package the buttons together so they only load once, hide them in some way by default, and provide a bunch of analytics. Lots of blogs and websites would pay for that - the current solutions for social button analytics are really bad, or non-existant (you need to know things like click-through rates, which share options are most popular, autohiding some for users who never use them, detect if the user is logged in for each service, how many followers/likes/retweets etc. each user gets from a share so you can identify 'power sharers' etc.) - I don't think that exists.

You can't just keep adding more and more buttons for each social service, and there are some people who will only use, for eg. delicious or pinboard and there are no buttons for them.