On a few of my websites I have created very basic networks of dofollow web 2.0 sites with articles and links back to my main site. When I look at backlinks to my site from either Yahoo Site Explorer or my Google Webmaster page I do not see a single link from any of the sites. These sites have been stewing for two months with little or no activity on my part. I would think that this would be plenty of time for the frequent indexing of these high PR sites to have yielded a link or two.
It leads me to wonder if the effort a person might put into building these sorts of links would be better spent writing articles, contributing to forums and exchanging blog posts.