Wordpress MU Blog Backlinks

I tried searching and couldn't find anything on this, but lately I've had some success using Google to hunt down WP MU blogs and create some backlinks.

Search term:
So for one of my Music niche's I did a search for that with +music attached. Found like 5-6 good networks with a PR3-6 on the main page.

A lot of the networks will give you a ******** link to your blog if you have a lot of posts, or are new, etc.

So for one blog I posted 5 posts/day for a week to get in the 'top 10 most updated blogs' on the network, which is a ******** link from a PR5 page to the blog using your blog name as the anchor text (which actually drove some good traffic too).

A lot of people know about this already, but for those that don't hopefully it gave you some ideas.

hello friend

i did also try to use this method in order to get a backlinks to my blog. my problem is sometimes i get an error message telling me that my email address (i.e gmail account) is not accepted. some of the MU blog accept my gmail account but after receive the activation key, it still cannot work and receive an error msg.

I have one question to you..how can we make sure that WP MU blogs is still active and related with our niche. For example : if i go to google and type inurl:"wp-signup.php", it will give me bunch of website for me to sign up and its very difficult to know whether the site is still work or not. What should i type on google in order for me to find WP MU blogs that related with my niche?

looking forward to hear from you.

peace