If you thought that spammy links on your comment section were not a big deal, well, think again. The official Google Webmaster Central blog published an article last week talking about this issue. Here is a quote from it:

Comments can be a really good source of information and an efficient way of engaging a site’s users in discussions. This valuable content should not be replaced by gibberish nonsense keywords and links.

For this reason there are many ways of securing your application and disincentivizing spammers.
• Disallow anonymous posting.
• Use CAPTCHAs and other methods to prevent automated comment spamming.
• Turn on comment moderation.
• Use the “nofollow” attribute for links in the comment field.
• Disallow hyperlinks in comments.
• Block comment pages using robots.txt or meta tags.

The article also warns against using blog comments as a link building strategy, which probably means that Google is scrutinizing more closely the links posted in blog comments now. This means one thing: posting hundreds of comments (either on dofollow or nofollow blogs) with tailored keywords would probably be a good idea, as it could get your site flagged for manipulative behavior.