Well I have skimmed the rules, and I love what they have done to the fighter (the only class I have read thoroughly), and the races. The focus seems to be to add some power at 1st level, avoid "dead" levels, and provide an incentive to stay with the 'vanilla' classes for a while longer.
I am a huge Paizo fan. I am GMing the Runelords adventure path at the moment, and have bought quite a few Paizo items. I will buy this RPG upon release, for sure, and will probably stick with it.
For me, there is an attraction in staying close to a set of rules I have learned: I just do not have time to learn another completely new set. I have a kid, a second on the way, a stressful job, and little free time. What I do have I like to use to play rather than relearning a new rule set.
3.5 is broke, a little. Hopefully this will fix those bits, but leave the core close to the original.
As for the commercial aspect - let us wait and see. I know I will support Paizo over WoTC, and I know I am not a hardcore gamer, but we shall see how things develop.
I think in 2010 I will be playing 2 games:
Pathfinder RPG
Dark Heresy
Although you never know!