The Propellerheads website
has info about Reason.
Personally, I can't stand the program. I find it annoyingly restricting and far too fiddly. I love the idea of having everything in one box, but I just can't come to terms with the Reason ethos. Hardware rack units are designed to fit into racks. Certain interfaces on units have small displays due to cost of manufacture. What does Reason do? Emulates these ridiculously tiny interfaces and wastes half of the screen. It makes the screenshots look good, but kills the usability. And obviously the MIDI/note editing doesn't hold a candle to B&P.
I'm downloading the v3.0 demo right now, but the blurb seems to suggest that they've just added some new effects units in there, and it still suffers from the same problems as the other versions.
Update: Yep, just like the previous versions. Not for me, I'm afraid.