Yes it's a beta, yes it's a little slow, and yes it's just a demo, but it is the first semi-functional PDF viewer on the market. It's buggy, but it's nice to see one of the many much wanted/much needed apps are arriving even before the January pay apps start. And no, I would not pay for this thing in it's current incarnation.
That's one thing I'm worried about with the pay apps. I would NEVER pay even a dollar for 2/3rds of the apps. in the market now. I really hope they get a lot better when we start paying for them. They should allow some sort of trial period so you can use the app for a day or something to make sure you like it before you buy it.