Nice idea in adding a no-follow attr to the links. But the current version (the very first one) does not support this feature. But you can do a small editing work to make it active.
Do the following steps
1. Open the socializer-socialbuttons.php file in the wp-socializer directory.
2. Goto line no 197
3. Replace the thing <a href= with <a rel="nofollow" href=
4. Similarly do this thing in line no 204 also.
5. Save and upload the file
Regards,
Aakash Chakravarthy