Doc,

You're not missing anything. There isn't a lot of information because it's not a tremendous deal. It costs something substantial to let somebody drive a car around for a day, so there is less margin of savings.

PL is useless IMHO for car rentals of more than four days because the weekly rates of the majors will usually beat Priceline's daily rate.

For longer rentals, I find the probabilities listed by Priceline misleading for their rental car screens because they end up comparing apples (daily rates) with oranges (weekly rentals).

While I've saved over $2500 in the last year on hotels with Priceline, I've had exactly one car rental with them.

Where I think PL may be useful is in bidding for specialty vehicles like vans and SUVs where regular rates are often very very high. But, I get my SUVs from National's Emerald Aisle, so I don't bother with it.