Link popularity is the fundamental concept of how major search engines rank sites in their SERP. This led to the abuse of this concept by the so-called link spammers in which blog comments are mostly targeted. To prevent the abuse, just over two years ago Google introduced the nofollow attribute. This is what Matt Cutts explained about it,
The rel=”nofollow” attribute is an easy way for a website to tell search engines that the website can’t or doesn’t want to vouch for a link. The best-known use for nofollow is blog comment spam, but the mechanism is completely general. Nofollow is recommended anywhere that links can’t be vouched for. If your logs analysis program shows referrers as hyperlinks, I’d recommend using nofollow on those links. If you have a wiki that anyone on the web can edit, I’d recommend nofollow on those links until you can find a way to trust those links. In general, if you have an application that allows others to add links, web spammers will eventually find your pages and start annoying you.
In combating blog comment spam, blog software providers including WordPress, Bloggers, LiveJournal and others have since supporting this by default.
Other than blogs, as a great resource Wikipedia is one of those web properties that had been suffering from link spamming. Basically everyone is allowed to freely edit or add links to it. This led to Wikipedia introducing the nofollow attribute to its all external links. This as a whole may have killed the concept behind link popularity as no one ever gets any link weights from this resourceful site!
To appeal, certain blogs (like Marketing Pilgrim) are very against this idea of Wikipedia and even went all the way to include nofollow attribute to all outgoing links to Wikipedia.
Further support of concept of link popularity can be seen. On his blog, Vinny Lingham even went on to install a piece of software (Do Follow plugin) to disable the WordPress default setting of the blog comments. This allows any comment links on his blog to pass link weights back to the original commentators.
Whether it is to no follow or do follow, as a blogger it is certainly your choice.