i have gotten good traffic from blog networks - there is a certain tactic I use tho, esp with top sites ones - ebook coming soon!
glad these questions have been answered. Common sense tells you really that links from mirror sites/blogs are ineffective, I would of thought blogs with duplicate content will disappear from the search results.
it has nothing to with databases, it's just that search engines can index blogs easily because of the feeds they offer
I've tried them a few times. The results are always the same. For lower competative keywords you will rise in the serps quickly (if you use those keywords in the link text). However because you get taken off of the front page of the blog very quickly, you start to drop in the serps within a few days. You are then left on a PR0 blog page that does you no real good. It remains to be seen if those interior pages will eventually get PR and do you some good. If you are using blogs it is much better to stick to blogs with a niche subject where the owner really cares about the content that goes on his blog. You will then get traffic as well as whatever PR benefit you may receive.
I agree about the blog networks being useless. I been on both ends selling and buying. I stop selling Cu's of the duplicate contents problem. I am in the process of creating 100 blog-networks.com but i will not add duplicate contents so that means it will cost a lot more than 30$ to get posts. I will charge a reasonable fee and as low as i can get it. Anyway, enough about my service. This thread is a very informative..I might add.