Finger drift is the nemesis of this otherwise wonderful product!
My experience is that you need either the tent stand, and plant your palms solidly on that at all times; or you need to put the flat device pretty far from the desk's leading edge so that only the elbows protrude and your whole lower arms rest solidly on the desk. Either method ensures that you're mostly using your fingers and wrists, not your arms, to move around the device, and this is essential. As soon as you've moved your arms, you've lost the game and you need to spend a second to "recalibrate" your hand position.
Even if you do this, you'll likely also need to recalibrate your fingers by resting them on the 10 dimples every couple of words (dongadoy forgot to count the thumb dimples). But that's easy to do because you're bound to have thinking pauses in your typing work, and you need it after gesturing too.
Shawn's suggestion to increase the V angle is also right; I think I could use just a few more degrees. I think the Microsoft keyboards have a slightly bigger angle than the TouchStream has.
Lastly, there is one hack you can do to actually provide more real tactile feedback -- make an overlay out of paper which has been creased between the key areas. You can print your favorite layout on the paper before you crease it. The paper needs to be thick so it won't wear out easily and also to make it more durable against finger moisture. I've described it at length here: viewtopic.php?f=2&t=2853#p5864