We landed late on a Sunday night and got to Dollar at 11pm. Even at that hour there were still 10-15 customers before us. I would say our total wait time was about 30-40 minutes, a bit longer than I've ever experienced at a car rental company (and especially at that hour).
My reservations were booked in advance online, so when I got to the counter it was pretty smooth from there on. The price at the time of reservation was the price I got at the counter.
It was my first experience with Dollar at LV, and will most likely be my last. It's hard to beat their prices (I paid $78 for a compact for 3 days), but if don't mind the lines to save a few bucks for the tables, more power to you.