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The +1 API documentation is here: http://code.google.com/apis/+1button/#jsapi
There is no mention of how to determine whether the viewing user has already clicked the button or not. This would be a very useful function because it would allow me to encourage people who haven't +1'd a page to do so without putting users who have already +1'd the page through a needless and possibly confusing step.
Has anyone found a way to do this? Thanks