Michael Martinez: As effective or ineffective as it is to get backlinks from any source. You have no way of measuring which links pass value. So instead of looking for links of a certain type you should creating the type of content you yourself would want to link to and share with others. And create visibility for that content by sharing it via social media, RSS feeds, advertising, etc.
Rob Woods: Depends on the site and the nature of the link. As Michael said above. From Twitter? Probably not very much. From a Wordpress site? Probably more. Ask yourself if Google would want the link to count. If the answer is no, then it probably doesn`t work very well. They are certainly more than sophisticated enough to know which 2.0 links they want to count and which they don`t. You aren`t going to "fool" them. Are the links really easy to get and scalable? If so, they probably give little to no benefit.