When using IE8, there is an unacceptable 6-10 sec delay between first-in-the-session's hovering over the AddThis button and appearance of Addthis menu.
The issue is not WP plugin-specific but rather IE8 browser-specific. (No such issue in IE9. No such issue when using IE8 with alternative sharing tools, e.g. AddToAny.)
Most curiously, the problem can be seen at AddThis own home page http://www.addthis.com/. Open it with IE8, hover over the iconic "red plus" button in the bottom-right corner of the big gray rectangle, and enjoy the 6-10 sec delay before you will see the appearance of Addthis menu.
I wonder if I'm the only person concerned with this problem? IE8 is presently about 30% of all installed browser base. I'd love to see a fix.