Depends on the forum and the directory.
Some forums are set to automatically "nofollow" links in forum posts. Some (such as this one) don't allow links to your own site within the body of your posts. Some prevent the search engine spiders from seeing signatures entirely, and others run signature links through a jump script to prevent them from passing any link benefit to the target site.
The point is, you can post and post in a forum, but -- depending on how the forum admin(s) have configured things -- you may or may not actually get any benefit out of it.
Directory submission can be a jump-start for a new site -- a way of getting those first few links that get the ball rolling -- but frankly most directories have such low-value interior pages (if they're allowed to pass link juice at all) they're not going to pass enough link value to make it worthwhile as an ongoing SEO technique, either.
In other words, once you've got an initial batch of directory links (assuming your initial batch is from directories of reasonable quality to start with) there's very little incremental benefit to be gained by spending hours submitting to a whole lot more of them.
As to blog comment spam.... errr, posting. Look, if your only purpose in posting a blog comment is as an "SEO technique" then you're doing it wrong. Post comments in blogs because you have something to contribute, not because you're trying to build links to your site.
Most good-quality blogs either "nofollow" links in comments, or they moderate comments to prevent obvious link drops from making it through. The ones that don't seem to care about link drops are, for the most part, not very good quality -- and thus don't have much link authority to pass along in the first place.
Of the things the OP listed, only article marketing -- either writing original content to be posted to your own site (a way of targeting additional keywords) and/or submitting to quality article directories (a way of spreading your content to other sites and potentially gaining some good inbound links) -- is actually a legitimate SEO technique.
The others are social media/social networking activities, and attempting to subvert them for SEO purposes will in many cases only annoy the community involved and potentially get you banned.
IMO, while they may
bring some SEO benefit, they are not intended to be (nor should they be approached as) "SEO" tactics.