I've been playing around with it every six months for the last five years or so. It's pretty cool, but astronomical units away from being "finished". Understandably, quite a lot of tweaked open source stuff works pretty well, and I can see it being a useful, familiar Windows-ish OS in another five years. But businesses aren't going to be flocking towards it any time soon.
They had a big hoo-hah a few years ago about disassembling binaries from Win2K, and then a long audit, which set things back considerably. And it the forum is full of "ZOMG I know Visual Basic so I'm gonna add 34 new features to ReactOS" kids who waste everyone's time.
Still, good luck to them!