Guys, keep in mind there are two different ways to track something like this.
1) check the ECU for an active tune.
Easily skirted with a piggyback device by just removing the device before going in for a warranty claim or service. If it's a tuned ECU, just flashing back to stock should do the trick unless they are checking the flash counter.
2) log performance data
This is NOT easily skirted. You guys make it sound like it takes a tremendous amount of engineering or hardware to accomplish this, but you could put together a solution for less than $5 in hardware. If they logged EVERYTHING your engine or transmission did, sure it would be complex and take a considerable amount of storage. But if all the log are are out of spec parameters, they need VERY little storage space. Think of it this way, if they were only logging the top 5 peak HP and torque instances to see if you'd tuned, they could fit all that in 8KB of space and still have tons of room left over. In comparison, a $5 1GB flash drive has about 1,000,000KB of space.
You are deluding yourself if you think this is all that hard or expensive for them to do
While I doubt you'd blow the engine unless you went crazy aggressive, there is a real possibility of running into transmission issues with much higher torque numbers. Remember, these trannies are rated for a certain amount of HP/torque they can handle, in fact the diesel and Hemi both use a different tranny from the V6 for this exact reason. And these transmissions are not cheap to fix or replace. The 7 spd in my current car runs 10k+ for replacement.
You can claim all day that it's no big deal and they would never do that, but it's all fun and games until you have a 10K transmission replacement the dealer won't cover. Go to any Audi forums and search for "TD1" and you'll see many instances of a car manufacturer denying warranty claims because of tunes, and they use a less robust system that's much easier to defeat...
"you gotta pay to play" is a quote used very often on the Audi forums as well, for this exact reason
For me, not worth the risk!