I like it, its good for getting relevent links, and great for indexing new sites. On the down side, links are not often given alot of weight in the SE's, and can be deleted by the site owner. I would use it as part of your overall link building, but not on its own. DD
Commenting can be very helpful if they are high PR blogs. Check and see the PR of the pages you are commenting on.
According to my experience, commenting are playing vital role for getting high and quality back links from relevant niche. It will be helpful to increasing page rank of your site. Good luck
Blog commenting is one of the good way to get traffic as well as backlinks. But blog must be do follow. Blogs index frequently by search engines. and they provide good backlink
What do you mean, commenting website? Are you talking about blogs? Like DomainDomain already said, this should be part of your overall link building. A mix of different kinds of links will always help you more as opposed to having links come from one source only (only blogs, only forums, only directories etc.) When you comment on blogs make sure to pick those with high PR, no nofollow attribute and a low number of outgoing links. These comments will be a lot more useful than some PR 0 nofollow blog that is spammed to death. And by the way I wouldn't recommend you to buy these "high PR dofollow blog lists", these often are auto-approve lists and even if you have to create an account on each blog to post a comment, these are heavily spammed and won't do you any good.
High PR (even better if the page is high PR), dofollow, auto-approve blogs can be very, very, hard to find. But if you can, they're a goldmine. If played right, blog commenting can be a great way to build high PR backlinks.