Flickr has recently added nofollow tags to the links present within its Web site observed Jeff Muendel & Brian Brown. This change came to light during a review of a Flickr account. The picture portal has long been considered one of the most attractive social media entities amongst few others for improving inbound links to a given site. The reason for this perception was simple that it continued to offer "link juice" from links placed within the user-generated content or the photo descriptions.
Perhaps the move comes up as a measure to forestall the ills of misuse and spamming. This would be the same reason for which the other social-media sites have taken this this meassure. Consequently, it somewhat dissolves the desirable charecterstic of passing on PageRank from yet another of mega social-media site.
Nevertheless, it's not a cause for too much anxiety as the nofollow tags have not been applied throughout the whole site. The links in Set and Collection descriptions are still free of them, but the links embedded in individual photo descriptions have been nofollowed. What would be the real impact of this step on SEOs only time will tell?
Since the nofollow links on Set and Collection descriptions have still not been implemented, coupled with the user profile pages could still get you the PageRank. While the SEOs may have to modify their strategy a bit but a lot can be achieved by building up good quality content, appropriate tagging and labeling of the photo, as good content can still drive traffic to your main site.
Moreover, Flickr has terms and conditions in place for any commercial usage of their service, so at the end of the day you might not want your account deleted on those charges. At the same time the fact remains that there quite a lot of marketing already happening on the portal, perhaps if your account looks more like a direct marketing effort then it sure is likely to raise a red flag. However, an indirect effort could still very well pass of as "legal."
This nofollow tagging act from Yahoo comes just after it had apparently, prevented crawlers from other major search engines from spidering delicious bookmards, see: Did Yahoo! Block Google From Crawling Delicious Bookmarks?.