These dofollow profile links are on a some high profile well known sites. There is much room for active participation in many of these sites. I undestand some people have been known to make multiple accounts but in truth a person will get better results if they make a completly filled out profile and participate at least some in whatever community is there.
Some of these sites have user blogs and those can be used much like article directories, or like Flickr have other types of content. Coupled with Guest Blogging , Videos, Article Directories, Bookmarking and blog commenting a person would get some pretty effective results. There are more ways, of course, but this stuff does work.
I have found it useful for driving targeted traffic to place content relevant to what I offer in these types of blogs. When I do a good job of pre-selling can work well to bring people who are already interested. Some people also build links to the profile with tools like Backlink Energizer
Quality trumps quantity in traffic as well as links.
Thanks to Jeff Quipp at Search Engine People for doing the research to evaluate these sites.