I considered the "Prepaid Legal", but instead tried the LegalZoom business legal plan, and found it to be very good. It doesn't have any "Membership" or "New account" fees, you pay each month for the month, and if you prepay for half a year or a year - they throw in a nice discount (15%).
So far I'm subscribed for less than a month, and had 2 attorney consultations and a document review. Although they didn't tell me anything I didn't know already, seems to be very cost-effective considering most people don't have sufficient legal knowledge or the ability to research.
It is, as @duffbeer703 mentioned, not an insurance, and if a legal matter arises that requires representation, their plan has almost no coverage, only discounts (as opposed to "Prepaid legal" plan that on the paper does have some representation). But to have 2-3 attorney consultations for $30 is definitely a bargain.