I'm just starting to do link building for my site. I plan on doing press releases and articles, but I also would like to know if the following will help my site in the SERPS:

Does leaving comments on blogs help at all?

How about posting at forums related to my sites subject matter?

Thanks for your help.

forum link drops are never liked... some allow signatures but most of those are no follows

To add to what Aussie said, lots of blogs also nofollow comment links.

It's best to focus on content that's of value to users and not spamming forums and/or blogs.

Thanks for the answers. And just FYI, I have no spamming intentions.

good man... then you should do well

I think both are good but you should focus on content that's of value to visitors and no spamming there.

If forum links and blog comments have nofollow tags, what is the point in posting in them in the first place, from an seo perspective i mean. Is it only for the traffic? If you say something relevant, users will be more likely to go visit your site?

seo perspective:

forum -> no because of no follow links
blog comments -> no because of no follow links
directory submission -> yes, because one way incoming link
article submission -> only to one page per article instead of all bunch of article directories