DNA as a Geneology Tool

Most of the time I'm sharing a link from Salon it's because they've managed to, yet again, shoot my blood pressure through the roof. Today is that rare, but wonderful, occasion when they've published something really interesting.
The book under review, Before the Dawn, sounds like a good read. I'm also fascinated by the idea of having my DNA evaluated. Being a history nut, and lucky enough to have inherited a lot of other people's work, I've got my geneology back to the first settlers in the US on both sides (male, German-1750, female, English-1690-ish but not the Mayflower). It's mostly all like that, German & English mixed together, but there's supposedly one Native American woman, and an Irish woman, on the direct tree. It'd be cool to find out for sure. $180 for the test is a bit high though. Other than that, it's basically a long line of farmers & workers with one known bad boy (my grandfather on my fathers side died of a "stomach ailment" that I later found was directly caused by that bullet he received during a fight in a bar).