I was wondering today that when we use SexyBookmarks of Wordpress or Blogger, does it hurt the SEO ?

Usually when we add widgets to Digg and re-Tweet our blog articles, the codes provided to add them right on the blogs is a javascript which is not indexed by google. Now this widget gives an images directly linked to these bookmarking sites with additional parameters of our blog automatically.
Example
I mean why would someone like Google to index these 7-8 unwanted url's under each article ?
I have added a rel="external nofollow" to each of these links but am unsure if that's what is needed ? I will update this article with that I find on the internet :D
Please leave your suggestions in your comments ?

Usually when we add widgets to Digg and re-Tweet our blog articles, the codes provided to add them right on the blogs is a javascript which is not indexed by google. Now this widget gives an images directly linked to these bookmarking sites with additional parameters of our blog automatically.
Example
I mean why would someone like Google to index these 7-8 unwanted url's under each article ?
I have added a rel="external nofollow" to each of these links but am unsure if that's what is needed ? I will update this article with that I find on the internet :D
Please leave your suggestions in your comments ?

Matt Cutts made a statement a year or so ago about the effects of "nofollow" and how Google had made changes to the way the spiders handled it...
Basically, a long story short is:
nofollow should mainly be used now in association with in-site links (faq,about,etc...) to prevent the spiders from indexing links that lead to useless information on YOUR domain.
However, they're "following" all external links now in an attempt to help reduce spammy link farms and so forth.
I agree but then what good do these links of digg, twitter and stumbleupon do ?
So I prefer doing a nofollow to these.
Moreover I researched and found that bigger blogs also do the same ... err... example Mashable !
Regards
Pushpinder