Chris Pirillo says what the rest of us have been thinking for awhile now:

In the past few days, I've been inundated with an enormous amount of subscribed search spam for designated keywords. To the tune of hundreds, if not THOUSANDS, of bunk entries. Who knew "lockergnome" and "pirillo" would be THAT popular?! Still, I can't help but think that others are having the same headaches - and 99% of the crap coming in is directly from a single domain: blogspot.com. Google, it may have been a smart acquisition in the beginning, but y'all need to clean house in a big way. You're the tallest nail, and you're really getting pounded - and now others, who aren't even using your service, are getting pounded. Blogspot has become nothing but a crapfarm, and your brand is going to go down with it. If your motto truly is to do no evil, then you need to start putting some resources behind an effort to curb this train wreck.

I don't know what's (specifically) making it so insanely easy for these spammers to get signed into your system, but you need to change that - ASAP. Forget about developing another Web-based aggregator for now (sorry, Shellen - Blogspot needs more help at this point). I'd love to ban / filter anything and everything that comes from blogspot.com, but the problem is that I have quite a few friends on that service who are sitting in the 1% "legitimate" minority.

As to why spammers go for that system, that's the simple part. It's free, and the signup process can be easily scripted. Which means that you can bot the whole thing, and create a universe of splogs within a few minutes. It's been a disaster waiting to happen, and now it's happening in a huge way.