Anyone have any experience with Geico?

I'm currently with <other big name insurance company> and I've not had any claims with them; I have a very clean driving record... and they offered me a whopping $5 discount on my 6 month premium. So I went and did a little shopping and Geico is nearly $250 cheaper for a lot more coverage and a lower deductible. I'm suspicious. :)

What's their deal? Are they 2nd rate? Or.. what? Will they triple my premiums in 6 months? ;)

The Internet reviews are mixed, people love 'em or hate 'em. What say you?