I used QNX extensively for a few projects at work, as it has historically been used quite a bit in the "automotive infotainment" world. I was really impressed by the overall clean architecture and documentation of the system, and I much prefer implementing device drivers in the QNX microkernel environment over implementing them in Linux, where interfaces are under-documented and always changing, and it's quite easy to lock up the entire system during driver development.

An interesting data point, though: QNX had a very clean and modularized 'microkernel-like' network stack called 'io-net'. But due to throughput issues in some situations, they switched to a new architecture a few years ago called 'io-pkt'. This is essentially the kernel networking code from BSD transplanted to a process in QNX; one advantage of this is that there's a large stock of drivers available to port and a lot of people are familiar with the BSD networking model, but some of the lesser-used corners of it weren't fully debugged when I was doing network protocol hacking, and in general it made me sad.

Anyway, you can definitely run full desktop environments on it, and you can especially run a full tablet environment if you buy a recent Blackberry tablet, as RIM now owns QNX and uses it as their latest Blackberry OS. This was, unfortunately, a step backwards in their openness and embrace of Open Source.