This reminds me of something that a group of exotic car owners used to do on California freeways back in the '80s. They would gather together and choose a highway to speed down. They'd send out spotters ahead of the main pack so that any John Laws could be located. They used CBs for communication. I don't know if that group still exists, but this is the late 00's version of the same thing.
Trapster uses location information supplied by cell phones (GPS) to tag areas where a cop might be hiding. I have to wonder how accurate and useful this service can truly be. GPS can be precise, but if the phones are relying on location information supplied by cell towers, the results won't be so specific. It might provide you with a general area in which a cop is hiding, but not an exact location. This means you'd have to slow down for a longer period of time. Then there's alert delivery to consider. Any delay in the network could prevent an alert from reaching a motorist in time, thus failing to help them slow down and avoid getting caught.
Another timing issue: longevity of the cops' locations. The stretch of Route 80 that passes close to my home in New Jersey is typically crawling with state troopers. But it's not like they sit still for long. We have plenty of fast-movers on the road to keep the troopers busy. What good will this system be if the cop's location is tagged, and they pull out five minutes later to chase someone who's not using Trapster? Trapster claims that its alerts are in real time and contain valid cop location information, but I just don't buy it.
Lastly, using cell phones -- whether for phone calls or messaging -- is illegal in a bunch of states. Using a cell phone to check for text messages while speeding down the highway (or city street) so you can avoid speeding tickets is just asking for trouble.
Either way, Tenereillo claims the business is booming, and that soccer moms are the heaviest users. Doing 50 in a 25 often results in a worse ticket than doing 70 in a 55.