GoogleGuy says that Google has recently made attempts to negate the effects of blog comment spamming.
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madone, you say in your initial message that you went around signing a lot of blogs, and now your site isn't doing as well as before. It could be one of two things: over the last few weeks, Google has started deploying better technology that negates the effect of blog comment spamming. The changes haven't fully rolled out yet, but it could be that your site just isn't doing as well now that the blog comments aren't doing your site any benefit anymore. The other possibility is that if you did enough blog comments to show up in the blacklist mentioned earlier, or if someone filed a spam report about your site, Google could have investigated, verified that the comments were done by the site in question (you admit this in your first post) and taken manual action to correct the spam.
I'd suggest that you read
especially the parts "Avoid tricks intended to improve search engine rankings." and "Don't participate in link schemes designed to increase your site's ranking or PageRank." Most of Google's effort in this area has been at updating our algorithms to spot and negate this type of spam automatically (i.e. no human in the loop). But Google does take blog comment spam seriously. If you really overdid it (and no offense, but by saying that you did it and that bloggers were sharing information about your site--that's pretty serious), then you could have triggered someone manually investigating. My hunch would be that our automatic algorithms just removed the blog comments links though, and now your site isn't doing as well. That's more likely.