The head of search spam in Google, Matt Cutts has recommended website owners who place widgets on the site or distribute widgets to place a nofollow link within the code of the widget. Matt has posted a video saying, "I would recommend putting a nofollow, especially on the widgets".
The video is in answer to question, “What should we do with embeddable codes in things like widgets and infographics? Should we include the rel="nofollow" by default? Advert the user that the code includes a link and give him the option of not including it?”
Cutts said that most of the people embedding widgets on their websites don't realize the other things that they are embedding on the website outside the functionality of the widget. Citing an example of poll widget in video, Matt said that if a widget is to embed a poll on the website, it might contain a link back to the poll website and that too without a nofollow link.
Matt Cutts is advising widget makers to add nofollow on the link so that PageRank doesn't get passed back to your site through the webmaster who is adding the widget code on the website. However, the links within widgets would not have the weight equal to that of a true editorial link.
Matt has also mentioned the example of embedding infographics on the website several times. Here's the link to the video: http://www.youtube.com/watch?feature=player_embedded&v=PvR_8aGEc98&t=0