Rented a Prius

Yes, it works for improved MPG. But it also works to decrease safety. In fact, the closer you get the better the fuel economy but the more unsafe it becomes. I suggest maintaining a safe and legal distance, and learn about other methods to improve fuel economy. There are many described in PC forums, some specific to the Prius, but others generic enough for any car, including your Camry. Spend a little time with the Search function.

 

Aside from the safety issues, drafting also increases your chances of front end dammage from road debris thrown up by trucks.

 

There definitely is some MPG advantage, but most people (myself included) feel that the gains are not worth the sacrifices (i.e. decreased safety, more driver stress, more possible debris damage, etc.).

 

Mythbuster's did study this and found a real improvement, though it is most impressive at unsafe following distances.

MythBusters (season 5) - Wikipedia, the free encyclopedia

55mph is equivalent to 80.67 feet per second, 65 mph is 95.33 fps. So 100 ft. would be greater than a 1 second following distance in this speed range. While in most places the legal following distance is 2-3 seconds, about as many people observe this as drive the legal speed limit. In most urban traffic setting, ~1 sec (or even less) seems typical. A lot of people only seem to leave 2-3 car lengths, which at highway speeds is less than 0.5s.

In general you will have much better braking capability than a semi, but you have decreased visibility into whats going on ahead which could affect your reaction time. Personally I find following a truck at ~1-2s safer and less stressful than dealing with all the yahoos riding up on your bumper and weaving in and out of traffic. If you're going to drive at or slightly above the speed limit, following a truck is a pretty good (and highly visible) excuse. Mileage improvement at this distance is probably only 5-10%, but thats not really why I'm doing it anyway.

Rob