I've just updated to Really Simple Share version 1.8.4, and the Google +1 button has disappeared from my posts. This seems to be a plugin conflict with CommentLuv Premium 18.104.22.168. For an ironic example, see this post on how to add a Google+1 button to your posts.
Any ideas on what might be causing this? I've also emailed the CommentLuv Premium author.