IMO yes.. and i always delete spam comments in my blog, especially the non relevant one

Use anti spam tools like akismat/spam karma 2, this will automatically kill most of the spams.

Yes. Spam comments can hurt you. In addition to the negative impacts to your site quality, Google recently announced that even no-follow links bleed PR.

It is funny that you mention akismat because in the original piece I read they talked about the spammers, especially the porn spammers, were becoming more sophisticated and had found some ways around the anti spam tools and they references akismat by name.

The problem I am running into now, and unfortunately no technical fix will help, is that my client is not keen on the idea of allowing visters to their blogs and website leave comments as they want total control over anything negative (instead of addressing each issue as it comes) and the thought that spammers can affect their sites will push them over the edge. I guess along with managing expectations some of us have to also managed fear and anxiety.

I have an option in one of my blogs where I hae to authorize every single comment. Some of legits but the majority are spam. I never authorize them. It is time consuming but it helps.

Well, after launching your blog and enabling the commenting option, a constant moderating and maintenance is going to be needed because many of the links people add to their posts might be pointing at low quality sites which need to be edited sometimes.

Spam commenting is definitely affect your website's ranking so check them and remove irrelevant comments.

yes, i believe that spam comments can hurt your site, if google or any search engine seen your site with a lot of irrelevant link, they will delete it.

Avoid spamming. It will really have a negative effect on your site.