Tracking, drivers, and game support are good. Unfortunately emagin themselves wrote a pretty basic driver that emulates mouse movement only (and thus only supports two axis). This is actually quite useful for games that don't support joysticks for view input axis (like fps or rpg games), but sucks considerably for flight sims. Thankfully a Z800 user wrote a program called ppjoyz800 which gives us a 'proper' driver to work with. It maps the Z800s 3 axis as a 3 axis joystick. So in games like AH2 you simply map the X axis to the x-axis-view (left right), and the y-axis to the the y-axis-view (up down). It needs a little centering to get things right but then you're done.

One of the nice things you can do with the ppjoyz800 driver is tweak the scaling. So you don't have to turn around completely to get a 6 view. For my setup it works at about 180:120 ratio. IE I look 120 degrees to the left or right and I am looking pack. 60 degrees gives me a left/right look. Sounds a bit wierd but it works well, and you don't end up with a sore neck (its amazing the amount of time I spend looking at my 6).
Tracking is very very smooth. It does tend to 'drift' a little, this is very common as between the headset, driver, and game things get off center a little. For this there is a configurable hotkey combo in ppjoyz800 to reset to centre. I have this mapped to a button on my joystick (if it gets off, I look to my real world forward, tap the button and everything is perfectly aligned again).
The 3 games I primarily use are Aces High 2, World War II Online (aka Battleground Europe), and Microsoft Flight Simulator X. All of these track smoothly.
OK, so we have the stereo 3D nailed, the 3 axis tracking explained, and the drivers what else do you need to know?
...HOTAS. You need a good HOTAS setup. And a backlit keyboard helps, with adjustable lighting. When you play with the visor its best experienced in a dark room. The less external distractions the more immersive it becomes. It also becomes easier for your eyes to focus/adjust to the headset itself. One of the biggest causes of VR sickness (which is nausea, and I've seen it happy to quite a few people) is flicking between looking into the visor then out the sides to the world around you. Dark environment = good.
But then dark environment + monitor off = where the **** is my keyboard. So a good HOTAS setup will make a world of difference. The less you need to reach for the keyboard the better. I'd also point out that this is one of the reasons I love trackballs, no groping for the mouse in the dark (no bestiality jokes please). The more stuff you can throw on the HOTAS the better. Its worth noting that the Z800 also means you can free up primary HAT from views to other functions.
I use a Saitek X45. Some examples of stuff I have mapped that are useful that you might normally map are (AH2) : zoom toggle ; zoom mapped to a rotory ; clipboard toggle ; icon cycle; autolevel; autoclimb (fixed angle); map zoom in/out.
Recently I added (thanks to some tips in the AH Hardware forum) mapping the Saiteks rudder/rocker to map to left right head movement (I don't use it as I have CH Pro Pedals). Wow, what a difference this made. One thing I did find annoying in AH is if you set your own view presets (eg, offset the 6 view to left or right) was the movement to the offset view the head took. You'd look back then your head would slide into position. With this new setting I could use the raw default head positions and use the rocker to look left right around the nose or back behind the seat.
Now, I can only imagine how awesome this would be with the 6DoF of a trackir adding x/y/z positional information so you could lean back forward, left right, up and down inside the cockpit.
Then theres the keyboard, I use a Saitek G15. It has backlit keys (blue) that have 3 settings, off, half bright, full bright. I usually play with the key light off, and switch to half if I need to type or chat. It is still difficult with the headset on, you can peer down through the gap at the bottom of the visor but I still end up with the odd mistake (I have a squaddie in WW2OL called thefsg, occasionally I hit the A instead of the S key... and call him, well you figure it out, I'm sure wonders about me sometimes).
With AH2 the headset makes the game a total experience, extremely immersive and loads of fun. Because AH2 has been written well with regards to head movements and 3D depth it makes setting up really really easy. Strapped into my headset with my HOTAS setup, I'm totally immersed in AH2. I'm seeing a true 3D world, able to glance to my left, right, up and down, with the views tracking to my every nuance. It is nothing short of awesome. I would spend more than half of my headset 'time' playing AH, I especially love the Squad Ops events and fighting in AvA where you get a more immersive experience. But there are other games too worth mentioning...
WW2Online:
Tracking is good in the aircraft. Not good for infantry, tanks etc (infantry view seems to be heavily limited in headmovement). Doesn't support stereoscopic or head movement.
Flight Simulator X:
Good tracking, supports stereoscopic and head movement.
Armed Assault:
Had a quick try. Was able to map the controller to view axis. Worked in stereoscopic, need to have a better play.
Oblivion The Elder Scrolls:
Doesn't support joystick for views so had to use the mouse driver. Supports Stereoscopic... and it was OMG experience. With the bumpmapping in 3D you get double the eyecandy experience.
Falcon 4:AF:
Doesn't support joystick for views so had to use the mouse driver. Didn't support stereoscopic (corrupted rendering). Found looking around with the mouseview difficult, constantly needed recentering.
Given the joystick and mouse emulation drivers there are many many other games out there (I understand theres a few driving nuts that use Z800s and love the Sterescopic 3D).
Real world video clips/demos of the Z800 (recorded with camcorder):
Aces High
http://renaissance.xtreme.net.nz/ms/ah-cockpit.swfFlight Sim X
http://renaissance.xtreme.net.nz/ms/fsx.swfWW2Online
http://renaissance.xtreme.net.nz/ms/ww2ol.swfcont'd...