There was a time when blog commenting, social bookmarking, forum posting used to work on niche related sites but now does it work any longer?
Sure, it does work! It has changed a little but still helps SEO or at least to drive traffic.
Just keep in mind:
if you create an article on someone's else website and have backlinks pointing to your site you might get a good link. However there is no guarantee. Just check if articles written by someone else in the same section are being indexed and what attribute links have.
if you just comment with your link most likely you might get couple hits to your site, but it won't be a good link. I call it ghost links. Most comments has
no followattributes and you might not even see it in your backlink portfolio.
I'd recommend you to focus on social media and social bookmarks. It helps SEO more than simple guest blogging/commenting.
Yes these methods are still beneficial for the SEO. Creating back link is good option for getting index to our websites. The back links from good forums make good result on SERP result.
These are good methods, but not the only. There is plenty to be found on this matter on Google, like link structures, fast loading and good content.