Blog comments still work. A couple of the biggest reasons that some ppl don't experience a greater success rate are as follows.
1.Short spammy comments. If you're a webmaster and you've logged into your wordpress blog what catches your eye the quickest and gets put in the spam can the quickest? Comments such as... "Wow great site!" "I found your site through a Google search" "What theme are you sing on your blog?"
These comments tend to be bog standard spam that comes with most SEO tools inbuilt. Do yourselves a favour delete this stuff! And write more targeted niche related comments!
2. Poorly spun comments that aren't readable will flag you as spam and will have a low success rate. To increase your success rate hand spin your comments. If your English is a bit shaky then add something like... "I'm sorry for my poor English as it's not my first language" then this will at least go some way explain to the webmaster why your comments are so grammatically incorrect.
3. Try to get links from ******** low OBL blogs. If you're using a tool like scrapebox you can filter them.
4.Go for blogs that are highly relevant with a high PR these will pass more link juice to your site.
5.If you're using an SEO tool do not blast too much. Drip feed as much as possible.
6.Do not spam the same domain multiple times unless you're posting on different topics and make sure your comments aren't all the same.
7. Create as many spun comments as you can and keep updating them and adding to your SEO tool.
8. Try using manual posting methods. Scrapebox has a manual poster which can be used for good quality highly targetted results,
9.When blog commenting always use multiple site URL's. Do not just use your single home page.
10. Do not overblast your money site. Make use of tiered link building strategies! Your money site should have a few good links to it, but don't overdo it!
11. Spin your comments well. If you don't you'll leave a footprint for other scrapebox users to follow.
12. When comment blasting make sure you use a wide diversity of blog platforms. Eg wordpress, blogengine, joomla, moveable type, image, guestbook etc.
Hope that helps.