I have done a lot of guest posting since our site went live. I just wanted to share some of the things I have learned
1) Big sites will take your work, even if you are small, so long as it is quality. (or in my case if you get lucky).
2) Blog in your niche. Guest posts at four digit Alexa, Google Page Rank 6 sites like Pro Blogger and Daily Blog Tips did not provide much of a traffic bump for me. Still a great experience, but I have had a lot more success with medium-big sized personal finance blogs.
3) Guest Blogging is the easiest way to gain new readers who will come back in the days to follow, in my opinion.
4) Comment on your guest blogs at other sites. Go to the commenters sites and leave comments.
You probably already know a lot of this, but just wanted to mention it for some of the other newer blogs. Happy guest blogging!