Seeing as the NDA has been lifted I can now post my review of iRacing here. I've spent a good few weeks with it and enjoyed it a lot. Here is what I've experienced.
The physics is fantastic. It feels every bit realistic. The immersion never fades and you never ask yourself "what the hell just happened?!". You can comfortably slide the car if you so wish. You can correct slides without too much difficulty. When you're at the limit and push further, grip is lost progressively rather than suddenly. It feels way way better than anything else I've ever tried in my sim racing experience (which is pretty much anything making a serious crack at realism in the past 4 years).
My oldish rig (3.0GHz P4 64bit, 1GB RAM, 6600GT 128MB Graphics card) it looks better than LFS and I get more FPS. What's more, FPS is much much more stable. In LFS, with 3 cars on screen FPS drops to half of what it is and is barely raceable. With 7 or 8 in iRacing, FPS drops from 80 to 65.
Netcode is something out of this world. I'm racing from South Africa, getting 400ms ping to the US. I don't see a hint of lag or warping. It's incredible - it looks like LFS single player. Hand on heart, I've had smoother races at 400ms in iRacing than at 40 in LFS.
Cars are every bit the driver's cars you want. The little Pontiac understeers most of the time but to get the goodness out of it you need to keep those gentle drifts going all the way through the corner. And it's got very limited setup options (none at all in the "rookie" version) so you can't dial it out. The Skip Barber R/T 2000 is superb and feels a lot like I'd expect a very low downforce single seater on road tyres to feel - drify. The Formula Mazda is a lot like the Formula XR or Formula BMW - slicks, and noticable downforce. Not my thing really, but if it's yours, you'd love it. And the Radical SR8 is genuinely terrifying to drive. What a blast, if you can keep it on the straight and narrow.
Car detail is superb. The setup options are exactly what they'd be in real life. They've taken measured values for suspension geometry. Interiors and minor details, everything is there.
The road tracks (ie. not oval) where I've spent most of my time are all fantastic bar one. Every one has had its surface laser scanned to make sure the bumps are in the right places and the slopes are at the right angles. And boy, does it make a difference. They're all American tracks except for Silverstone. Laguna Seca and Lime Rock Park you probably know from other sims, but Virginia International Raceway and Infeneon Raceway are no less challenging. A real blast to drive - in all the cars. Who knew the yanks could make such tracks - complex corner sequences, blind corners, ridiculous cambers, all the boxes are ticked.
The sound is great. I tend to shift the little Pontiac up more than I need to just so I can hear the noise of a heel-toe. In the Skip Barber you can hear the engine coming from one side and the exhaust from the other. I used to swear by synthisised sounds but done properly, sampled ones are very very good indeed.
And to top it off, iRacing's online system is superb. You get what's called a safety rating - it's affected by your online racing. It takes into account crashes, loss of control and track offs. And it works, it's never wrong. If you have too many crashes, your safety rating drops and you can't race in the more advanced series. It's a real motivation to get better.
Each series also comes with a bunch of different servers. There are servers for practice which don't affect saftey rating (the only online sessions that don't) - it's basically just so you can get the hang of wheel-to-wheel action. Also, time trials. You have to set a certain number of incident free consecutive laps (different for different tracks - it was 4 at Laguna Seca and 8 at Lime Rock Park for instance). The people at the top of the charts at the end of the week get some points for that series. Then the track usually gets changed and the charts cleared. There are also qualifying sessions. You go on a qualifying server and set a time. It counts for the whole week and you're gridded on a race server based on that time. You can improve your time as many times as you want - the advantage of pickup racing and the advantage of an ordered grid, all in one. Race sessions start every 2 hours or so (depending on the series - you can obviously switch between series so that doesn't limit your racing to one race every 2 hours). Races start with a warmup session which is quick and helpful and last at least 25 minutes or so which gives it a more serious feel than just 5 lappers.
There is also a great professional racing feel to it. They have a nice flagging system. If you cut the track, you are cautioned and asked to slow down for a moment. If you don't comply, you are black flagged. At the end of each race, you can see detailed results (sort of like LFS-stats).
So is iRacing worth the money? You bet. Every penny. Just a shame that I'll be on a student budget over the next few years and I won't be able to afford it. I need to research what organs I can sell and go without.