I bought this car in March of 2006. I wasn't even looking for a new car at the time, but this one was everything I had ever wanted in a grand prix - black, charcoal leather interior, HUD, sunroof, Bose, chrome torque-star wheels, you name it, and it was there. I test drove it, and bought it the next day. Going from a 4 banger hon-duh with the complete rice treatment (fart pipe exhaust, intake, lowered, etc... bought it that way, regretted every day of it), there was absolutely no comparison. This thing gave me goosebumps when I first drove it.
For a big, chubby, heavy car, this thing scoots! The torque is there instantly thanks to the supercharger, and the power doesn't fall off until you wind it out into the upper 5000 RPM range. I've already surprised several mustangs, ricers, and other supposedly "faster" cars, much to their dismay, and this GTP is still completely stock except for a fender-well intake that I fabricated myself, and performance tune. Without the baffles that the stock intake has, the flow restrictions are eliminated and the supercharger screams! Very cool, and it scares the people next to you when you race :)
The only real downside is the fuel the car needs. Being that the car is supercharged, it runs on premium only. And, since I love my car to death, I only run Shell V-Power in it, so my fuel costs are pretty high. However, this car gets INCREDIBLE highway mileage for a supercharged V6 - I averaged nearly 25 mpg on a trip from Toledo, OH to Denver, CO. Once I was out in Denver, I got a custom performance PCM tune done (reprogramming the fuel trims, timing, etc). This boosted my power slightly and increased my highway mileage to nearly 28 MPG! If you want to call BS, fine - I'll link you to a picture of my DIC. Of course, if you have your foot to the floor, you'll average about 15...but if you set the cruise control, you'll get very impressive gas mileage with plenty of power on tap when you need it.
The interior is typical pontiac, although I think that the Grand Prixs are nicer than most. Although the plastic is a little bit cheesy, it seems to be well put together, and it doesnt creak or squeak. Being that the car already has 60K miles on it, I figure that if the interior was going to make any noises at all, they would have emerged up by now. I'm happy to say that to this day, there are none. The doors are leather trimmed in certain areas to match the seats, which looks very nice. The guages glow a nice shade of red, again typical pontiac, something that I've come to really like. The Bose system seemed a little underpowered to me at first, but after tweaking it a little, I really like it. Enough bass to sound good without distorting, and enough high end to sound crisp. The heads up display is a gem that I probably couldnt live without now that I'm used to it...and I need it, too. I'm a fast driver, so it helps to be able to just glance down to check my speed without really taking my eyes off the road. The display has started to fade a little though, but I've heard that this can be remedied by re-soldering a contact in the HUD unit itself. Not a difficult task, I just haven't gotten around to it yet - besides, the HUD isn't dim enough to really bother me.
All of the controls are well laid out and easy to reach, and the seats are very cushy and comfortable, although there isn't much side support for agressive driving. This is great for the lazy drivers that go slow...but for the more spirited guys and gals out there, tighten up that seatbelt or your gonna slide around a little bitin the hard corners. All in all, I love this car and will probably keep it well into the future. With the right modifications, these can be extemely fast vehicles, while still being very reliable. I know of several daily-driven 12 second L67 powered vehicles (two being grand prixs, the other being a Regal GS - both cars share the same drivetrain).
To the people who have had poor experiences with these cars - you got lemons, ladies and gents. Plain and simple. Sorry for your bad luck, but every manufacturer has lemons. If anyone out there is considering buying one of these cars - DO IT! And get the GTP, its very, very worth it to have the L67 engine with the supercharger...