I use WP 3.1.1. and Addthis plugin 2.0.6 (same problem in 2.0.4 version).
The Facebook's display counter appears like that:
And with Firebug I found the problem at the "iframe" of the Facebook's button. The "width" is 90px and if you put 100px is solved:
But this iframe code doesn't appear at WP Plugin editor and then I can't fix this problem.
Any idea? Thanks!