Did you ever come across as comment that you know is promoting a product but for unexplained reasons you go ahead and approved it? I just did. The comment is well crafted that it made me question my definition of a comment spam.
The idea of effective link building by commenting hit me. I don’t know why others still use bots to leave meaningless and irrelevant comments on blog posts when they could do so by doing it manually. It’s time consuming, yes. But it’s way more effective than bots. Akismet and other bayesian filters has done a good job detecting and stopping automated commenting. On my blogs, akismet has effectively stopped spams except for a very few which I guess was due to newer spam parameters akismet still have no record of.
But looking for relevant posts in technorati and writing a good line or two of comment will probably get it approved.