I don't allow them posted in the first place. I use Wordpress with Akismet enabled with a couple of options like "New comments or comments with links should be sent to moderation queue before they appear on the blog.

So, No chance to spammers at all!

BTW, I don't know if they affect your site rankings since I haven't experienced such kind of situation. May be that's another unproven SEO theory.

When discussing link building strategies in SEO, Google has started using language like: "These are typically useless exercises that don't affect your ranking in the results of the major search engines -- at least, not in a way you would likely consider to be positive.".

In this same way, I would think that blog pages that are improperly maintained (harboring link spam in the form of comments) are subject to some form of damper penalty or at least non-rewarded.

Yes some spam can have harmful attachment when you open them open and can spread into your harddrive.

We're back to no-follows not bleeding PR.

http://blog.search-mojo.com/2009/06/...ges-at-google/

Blog comments are safe. Now you just need to deal with the spammy aspect.

Spam comments can discourage your reader, but in some cases, they "may" affect search engine rankings.

Have moderation of the comments and post them only if you like and/or remove the links(or other spam content) and publish what part you like =))

Yes, spamming over the site hurts in many ways, it affects the quality of the site, visitors never turn again over it. I prefer to filter the comments manually instead of using akismat/spam karma 2 like software.

A new wrinkle to the original questions is what about the type of spam that I see around DaniWeb occaisionally. This would be the post is helpful and informative but the poster also throws a link in promoting their business. DaniWeb is clear about this type of posting activity, as I am sure many other sites are, but still it is done and the moderators have to go in and edit. Does anyone know of a utility that can be used that would block the placing of URLs in comments or at the very least allow the comment and block any url?