That's what I was asking, if you used blogs such as free hosted one, like the ones you mentioned. I asked because those type are usually quicker to show up in the ranks because they are powerful popular sites.
Alex gave plenty of good advice. Though, many might call them web 2.0 sites, same thing I guess. Or some call them social sites. But yes, as he pointed out, they are all worth posting too. If your mainly looking for back links, post to every one you can find, with the right anchor text, that's important. Blogger by google is another good one.
I've had bad luck with Wordpress hosted blogs, they deleted three I made, they don't like promotional type blogs. Which is fine, their site, their rules, understandable.
Another big question, how are you checking back links? Google has been way off for years. Yahoo site explorer is the most accurate I use.
I personally don't keep track of backlinks, I just keep track of my ranks for my keywords, that is my end goal. From where I rank, I know what needs more "juice". About the only time I check is when some one is beating me in the ranks, see what they are doing.
Another powerful link back tactic that few seem to use or realize is RSS feeds. To me, an RSS feed for your site is as important, or slightly more important than a site map.
RSS feeds gives you something else to submit to places you wouldn't normally submit your site, such as RSS directories. Your feeds can also get picked up and published by others, usually scrappers, but it's still link backs.
Many social sites such as mybloglog, multiply, even blogger blogs allow you to add a rss feed to your "profile". This of course means, as your feed updates on your site, as you add new content, the feed info is also updated on the social sites you placed it, automatically. The big key is it gives you deeper links that you might not normally receive, or have the time for.
A number of social sites also generate rss feeds for your "profile". Once you have your info in, you could submit those feeds to places like pingomatic. Get the SE's finding your back links even quicker.
Even with twitter you can use twitter feeds to add your RSS. Every time you add content or your feed is updated, it automatically posts to your twitter account. Great for bloggers, and a time saver.
I have an add-on for firefox, where I can right click and click on nofollow, it shows if links are nofollow or not. Again if you looking for back links it could keep you from wasting time on a social site that in the end, won't provide you with back links.
Guess I ramble too much myself. Hope some one will find it useful