In getting feedback on my proposed bloglist page on the MSDN Web Services Developer Center, Danny Ayers mentioned that I had an equivalent signal to noise ratio as Sam Ruby and yet I am considering dropping Sam from the list. I don't see that combining two different evaluations is a particularly useful measure. I would much rather follow a blog that has a low signal and little noise than follow a blog that is high signal and high noise.
I think the various readers out there also do a great job of making low-signal blogs easy to deal with. High-noise blogs on the other hand are not as easily dealt with (unless you call dropping them an easy means of dealing with them). I know there are efforts to categorize blog entries (as I do on my blog) but I don't see these efforts as being a particularly successful way today of limiting noisy blogs.
Frankly, the best blogs have a little noise. I want it to be mostly on topic, but I also want to get to know the person as well.