The issue is illustrated in this picture. It's the custom field 'sociable' displaying where it should not, at least not as I understood the use of custom fields, when I read "custom fields can be used to add extra metadata to a post that you can use in your theme", and as illustrated on using custom fields. The reason I linked to Trouble with Custom Fields in 2.0 is because I think it's somehow a related problem, and people were indicating key values could be hidden, which can perhaps been done in the plugin, instead of in the wp core files. The problem, where _encloseme, _pingme and _wp_page_template were visible, where they shouldn't have been, was solved in later version of wp by the way, but now seems to be back for your key (sociable).
One more thing, since this problem only popped up after having upgraded to wp 2.7, and the latest version of sociable, and not before, even though I was using the exact same code in my post template, something must have changed in either wp 2.7, or in the sociable plugin itself.
I imagine other users that are using custom fields might experience the same problem. Perhaps there is another plugin doing pretty much the same as yours without having this problem, but since I have been using this one for quite some time, I thought I'd signal the problem instead of just using another plugin.