alika - 1:44 pm on Jun 30, 2010 (gmt 0)
In our case, 44% of AddThis use is to email the content. Only 10% are favorites and 9% used for Facebook. Until we can have a more robust Email to a Friend script (prior to Addthis, we used a script but was spammed to death), we'll use AddThis.
We never saw a decrease in traffic from search engines or attribute any change in PR with our use of AddThis.