I'd be surprised if a link in the comments has much worth even if it is "do follow". Google knows which part of the page a link is in and can discern between in content links and those peripheral to the content. The links that *really* count are to be found inside the content. Not saying that the comment links aren't worth anything. Probably quite useful when starting out to get a site discovered by google and indexed but beyond that you are going to need an awful lot of them for them to be of any use.