Not one of the three blog search engines listed above do a very good job, if any job at all, of blocking blog spam. Do a search for some sports gear, like “wrestling shoes”, and there is a great probability that more than a few results in the top ten are spam blogs.
Why is this? Is it that hard to filter out spam blogs? Maybe. If so, what I suggest is a flagging system much like Blogger.com has. If you think a blog is bad, flag it. Then someone (or so we think) will evaluate it and decide if it should be removed or not.
I know that filtering out spam is probably a big headache, but it’s something that is tarnishing each one of these blog search engines.
It should be quality over quantity, not the other way around.
One note: I have contacted Sphere and Technorati recently. Sphere said they were thinking about adding some sort of user defined spam reporting and I’ve yet to hear back from Technorati.