One of the things I do know about Google is that they have some very, very clever people there. If you think up some idea which you think will game the system, they’re almost certainly way ahead of you.
Now, we all know that links from other websites are key to getting your pages to rank highly in Google. And if you go for a long walk and try to think up ways to generate links, it’ll only be a matter of time before you come up with the idea of going to people’s blogs and mentioning your site in their comments there. Guess what? They’ve already thought of that. In Hard Facts About Comment Spam on the Webmaster Central blog, they tell you that it won’t work, but they also hint about why: it’s all about patterns of links. Google has so much data that it can see natural patterns, and it can see unnatural ones.
It turns out that to gain any benefit in the search engine results from spammy links from blog comment sections, you’d need thousands of them. So if you put the odd one in here and there, it’s unlikely to gain you any reward anyway. There’s software you can buy for a few pounds which will “comment spam” your links on to literally millions of websites. Google knows how to ignore that stuff, so it’s fairly obvious that it’ll ignore anything you do “manually”.
Occasional informed, intelligent comments with a deep link to your own website – that’s a different matter.