Two cousins have posted this on their blogs. I figured I'd try it out too...
Postgrad. So that's cool, I guess. But then I decided to try out www.seriouslysoblessed.blogspot.com, and it gave it a genius level. Admittedly, it is genius, but it parodies dumbness, so any ranking site like this should give it a low rating. That, and I'm sure the fictional TAMN would be horrified that her site warrants a genius ranking. Orson Scott Card's website warranted an "elementary school" reading level. Ouch.
My final analysis: I think this website hands out rankings on a random basis. It remembers what it handed out, so if you type in the same website twice, it will give you the same answer both times, but it's still random. I tried it out on some friends blogs too...and friends that write on a higher level than I do got lower rankings.
Also notice (but don't click on) the tiny writing on the bottom of the rating (where it says "TV Reviews"). This, no doubt, is why the blog readability test exists. It's basically an advertisement.
Feel free to try it out. Just remember, though...it may be fun, but it's most definitely BS.