I'm blogging this with a friend's Das Keyboard. So far I don't miss the letters on the keys at all. We'll see in a short bit when I start coding some Python though.
They claim 100% improvement in typing speed, and I can see how it might work that way. On the very few occasions that I am tempted to glance at the keyboard I'm not rewarded so I've learned to quit doing it.
At $90 I'm not sure I'll buy one soon, but I think it's now on my would like to have someday list. The tactile feel of the keys is reminiscent of the old IBM keyboards, but with slightly less resistance.