I never actually rented from Dollar/Thrifty myself; I was the middle man when my sister needed a rental a few weeks ago (can't remember exactly why she couldn't call herself).
Since I made the reservation for her over the phone, all my sister had to do was go to the main building (on Belvedere) to pick up the car and sign all the necessary paperwork. However, if you're flying into PBI and need a rental car, you can reserve from the airport counter and take their shuttle to pick up the car.
Obviously I can't comment on the actual pick up or drop off, or cleanliness of the car, but the CSR I talked with on the phone was courteous, informative, and didn't pressure me into upgrading -- she looked up the car I asked, gave me a quote, and made the reservation. Done.
I can only give this a "good" rating because I didn't go through the whole rental experience, but I didn't hear anything negative from my sister -- maybe she'll make a review here on JB -- or maybe she already did.