I got it for christmas, it's awesome kit. Works best in ArmA(2) and rFactor and I'm told it is perfect for Flight Sims, so much so that the community swear by it. You can zoom into the knobs and look around the cokpit and press the swicthes unreachable by default. In ArmA you can look around you as you are on patrol, to help immersion (in a not so immersive game). You can stay with your ironsighst marked on an enemy soldier, as you look to your side to wait for your men to get into position.
In racing sims, it hasn't peaked yet. In GTRE/Race 07, there are these little limitaions when you turn your head so far the camera just stops. It gets a little annoying and you can't see completely to your side. In rF, there are no limitations, so you can turn your head as far in the game as in real life. This is great in netKarPro for the same reason as the flightsim, you can get around the cokpit and press the switches easier (I like the whole buttons and switches system) but the limitations are woeful in nKP, you can only turn about 10 degrees and it stops. As far as I can tell, it doesn't make you faster, and it can takle time to get used to and you may be slower, but it frees up buttons and makes looking around alot smoother and easy so you dion't lose focus. It also helps when drivers are passing you, I swear by it as you can see where the drivers are easier (unless there's a blindspot, like the Cats).
You can get TIR4 cheaper now with the 5th version out, but even the 5th is cheap enough considering the tech. Itis good value. More and more games are adopting it, but it all depends on what games you play and what you want from TIR. Just to note, it will take time to change the settings to your preference, and some games like Race 07 done support it as well as other game, and you will need the hotkey to centre it after a couple of laps. Still, no biggie. With the newer sims, they will support TIR better I hope.
Hope this helps