> - How can GNOME measure its success to know they're heading the right way?
For the "right way" they actually do user testing / design / trying to simplify specific workflows for an average person. You'll hear about it sometimes on the mailing lists, but if they publish anything it's usually only the result. While the lack of opennes there is annoying, at least they're doing something.
> If it's the number of users, how can it gather usage data?
I hope that the downloads per version and per distribution that uses gnome3 gives some data. (although it's dirty data, affected by many other effects)
> - GNOME seems to focus on being great on touch devices, but how will they end up on those devices if they don't sell hardware?
Yeah... that's the question I'd really like to find the answer to. Maybe the idea is that normal desktops will just become touch devices in some time (HP Touchsmart / MS Surface style). But that's a gamble and I haven't seen that claim made officially yet.