I have one at home that I use as my daily keyboard. It's pretty cool. One very nice thing is how quiet it is, especially with a 'skin' on it.
One thing I really don't like about it is the lack of utilisation of the thumbs. I've been getting pain in (especially) my left thumb joint. I believe it's due to having to curl my thumb in to get to the meta / alt / windows keys.
This was really bad on my work Microsoft keyboard, but isn't great on my typematrix either.
I just got a second hand Kinesis Advantage keyboard for work, and really really like the thumb sections, and also the remapping support. In less than a week my thumb pain has cleared up quite a lot.
I also really wish that the two sections on the typematrix were angled a bit outwards. It seems to work OK, since it's in rows it's a lot better than normal keyboards, but I feel that being able to spread my hands apart would be a good thing.
I really really like the remapping support on the Kinesis advantage.
I'm using the workman keyboard layout ( http://workmanlayout.com/ ) which seems to work very well for me. The biggest downside is the lack of native support for it. On the Advantage, I remapped it in about 45 seconds total, and now that keyboard works anywhere I plug it in, without needing any setup.
Otherwise, though, I'm pretty happy with my typematrix. My wrist angles are waaay better than they ever were on a normal staggered qwerty keyboard. And it's so quiet I can type while my wife and baby are asleep on the couch right next to me without disturbing them. That certainly wasn't the case with my MS keyboards.
I also really like how little desktop space it takes up - the mouse is now a lot closer and doesn't need a huge reach over to the side to pick up.