I have heard that it is a good idea to post comments to related blogs. Is this effective? Does it really help or is it a waste of time?
Its good for traffic as long as your not posting spammy comments that will get deleted. But most blogs have a default setting that has a nofollow tag on links in comments now so it wont do you much for SEO.
No follow is ignored by some seach engines, I believe Yahoo ignores it. If your message is relevant then the link will stay and be useful, for traffic, SEO and PR. If you have a relevant article and link to it the blogger might even write about it... if your lucky.
Links are always welcome, no matter where they come from. Links from blogs could create some traffic, it all depends on the blog a on quality and natural look of your comment. p.l.u.r.