As I hav ethis toy for more than week, I can share a little more information about it. Please note that some experiences are based on fact that this is my first "big" phone with touchscreen.
The big screen is great for reading. Much better than my old Nokia E52. It is also much better readable on direct sun light. The dark side of this is of course power consumption, but I think this might still get improved for production pieces.
Having Linux on the phone is nice, ssh to phone and you can do anything comfortably with real keyboard (N950's QWERTY keyboard is great, but still quite small). Having Debian based system there is even better, though I felt a bit strange when I first ran apt-get upgrade on my phone :-). Well there are some changes from standard Debian system like extented fields in debian/control for icons, but generally it feels pretty much as Debian.
There are lot of things to try on N950, you can find some hints on N950 landing page, I still need to try most of that :-).
It's just too bad the N950 cannot be purchased and won't be sold :(