Well, I gave this thing a fair shot at about a week and a half but ultimately decided to return it to Amazon.
Honestly, I wanted to like this, I really did, and I do like the idea of it and the direction that Samsung is headed in. Unfortunately, there are very few practical reasons to own one of these at this point. While it does do a good job of replicating the desktop experience, it just feels way too much of a "beta product". I kind of feel the same way about the Gear VR, but with that I feel like its grown into being something that is sort of worth the money to have.
The main issue with the Dex isn't so much the lack of "dex optimized" apps, its the way that any app (even the dex ones) work. I HATED the fact that any time you open a link to a new page on a website that it would open up in a new window entirely (except that in Dex instead of a new window you get a second app running at the same time.) There are several other nitpicks but this one really drove me crazy.
All in all, Dex DOES work and it could be really useful down the road if Samsung even continues with it...who knows. It doesn't seem like its getting much attention so I'll be surprised if we see it again. Its got some potential though if they do pursue it...