Yeah, I have to agree with soapdeli on the followers thing. Google Friend Connect is one of dozens of ways to follow blogs, and not necessarily a good indication of the amount of traffic a blog gets. I only have 350 followers through GFG - but my blog had 27,000 page views and over 7,200 unique visitors in April, and continues to grow. Any blog offering sponsorship should have these stats available to you.
Look for blogs that are in the same niche as you you and/or ones that have readers in the same audience you market to. I do advertise on a couple of other independent blogs and have had good results, and almost all the sponsors on my blog renew every month... I think it just takes a bit of research and trial and error, and it can definitely be worth it.
xo,
melissa
www.bubbyandbean.com