About 10 days ago, Google published a post about comment spam on their WebmasterCentral blog. They have warned that they have the means for understanding the link graph & they can determine and tackle comment spam links using algorithmic methods. They can even determine the fine-line spams that some webmasters deploy like instead of blunt spam they will say “great site!” as a comment with a keyword as their name. So in best case, you will receive a little or no SEO value at all for posting meaningless comments in other websites & blogs.
But still I doubt if spammers will stop spamming. These may be hard facts about comment spam, but comment spammers are hard nuts to crack. They perhaps just like to spam 
Comment spamming will bring a bad name for the web site… i hate spammers, every day my plugins are blocking hundreds of spam comments!
I am tempted to write simply ‘great site!’…
However, I too hate spam with a passion, spammers are too stupid to realise very quickly that their tactic is not working – hopefully, this will also leave spam software sellers high and dry, although they will no doubt still try and sell their crap.
There is clever black-hat, and then there are the wanna-be black-hatters who have no real idea about what is really going on – they are the real nuisance…
I do not see how any of the spam gets actualy approved unless the webmaster is not using any anti spam blocker.
Or even worste yet if they are not even looking at the blog after they make it.
So each any every day I delete about 30-50 spam posts.