I did some experimenting with FreeTrack a while ago. As you'll know, for FreeTrack all you need is a webcam on your PC + an LED somehow strapped to your head. (one LED --> two degrees of freedom, while three LEDs --> six degrees of freedom). I was using just one visible LED. The results were mediocre at best, but they sparked my interest. I knew it was possible to make your own tracking device, but I have no clue about soldering and stuff, so I kind of discarded the whole thing.
Then, recently, I stumbled upon a guy in the US selling pre-built caps with built-in infrared LEDs. I thought it would end up being terribly expensive, but I only paid a little over $20 (shipping included), and with the weak dollar these days it became very affordable. Here are some pics:
I haven't had a chance to try it with LFS yet as I'm on vacation, but I'm totally blown away by how well it performs in flight sims. Since the LEDs are infrared, I've strapped on a visible light filter in front of my webcam to avoid too much background noise interfering with the tracking (just a piece of the inside of a floppy disk -- it's great for the job!). The tracking is flawless and responsive, and the cap is very comfortable. Can't wait to try it out with LFS!
I know that the TrackIR-fans keep saying that their system is better because it has more FPS than a normal webcam can allow. But seriously, I notice absolutely no lag at all. 30FPS is more than enough for smooth, precise movement. And the next version of FreeTrack will also include support for using a WiiMote instead of a webcam for tracking, which gives you 120FPS. Plus, FreeTrack is -- well -- free.
All in all, I'm extremely positively surprised at how well both the software, and particularly the cap, are working. I'd definitely recommend you guys to give it a go. If someone wants the contact information to the guy making the cap, just drop me a PM.