i used the two, mybloglod and blogcatalog. and it seem work well to me. even you need to spend your lazy time to do this or that there, it will help you socialize better. but, people said that entrecard is also the effective way. so, why don't you let the 3 work for your blog(s), it must be great.
I help allot of my friends out with promotions and whatnot.. so I'm usually on trig.com. It's a pretty good community if you like a diverse range of music. They filter it so it's not just a bunch of myspace bands
I used Blogrush, its concept is very good somehow it was not driving any traffic. Do you find it effective?