There are certain techniques, whether blackhat or whitehat that are very reliable and are done on regular basis, like non-reciprocal link exchanges, article publishing and distribution, social bookmarking, but what about DoFollow blog commenting and forum signature posting? Are they still worth something?

DoFollow blog commenting may be helpful but once the blog posts goes inside the page the backlinks may get devalued.

What blackhat techniques do you consider very reliable?

DoFollow Blogs are very popular for extra exposure. I've no applied it in the web hosting field, but I have many customers, which utilize the technique daily and it works well for them.

OK, my bad, I have used a bad term. It should be "effective" instead. Also, I think that every technique, even whitehat, can be considered blackhat if used excessively.

About DoFollow commenting... If page where you left your comment was tagged, for example, with 5 tags, belongs to 1 or 2 categories, and can be found in archive under its publishing date (day, month, year), then you have about 10 pages linking to you from that blog. I remember posting a single comment on a blog and receiving about 20 backlinks (as seen by YahooExplorer). So it does not matter that much if post gets inside the blog (off the home page). Although it is good to remain on the home page at least while the robot index it.

And what about forum signature posting, opinions?

I may do a little experiment by promoting one of my new sites only with DoFollow commenting to see where it will get me. This can be a good way to see whether this is working.

I've found forum signatures to be somewhat helpful. Don't know much about this NoFollow business, but I'm interested.

Found this just now related to Do Follow Forum Signatures. I was immediately drawn to forums I'm subscribed to. What I have noticed is that posts from more active forums are indexed very quickly on Google. Often, when searching on a hosting related question, I'll find a link on the first page leading back to a thread on a forum posted just minutes earlier.

Yeah, it seems like a lot of people don't think forums are helpful, but that's what I've found too.