The expected %age of blog comments accepted is covered quite concisely in
this thread.
Basically keyword choice makes a large amount of difference in how many comments will be accepted, as does PR/OBL/Bad Words limits, proxy settings and many other things. The most likely culprits are the proxies, keywords and limits though.
If you are not using private proxies or proxies harvested using a third party tool then you will be hindered, currently the inbuilt proxy harvester is overloaded by so many users (currently a heck of a lot of trial users for some reason) and it is making it harder for the tool to find unique qorking proxies for everyone which means it is harder to get search results and therefore less time is spent searching. I think most users would be absolutely astounded by how much of a huge difference using private proxies or proxies harvested with a purpose built tool.