After installing, with no problems, one of our main Windows desktop applications and running it occasionally for over a month, I've been pleased as punch with the Windows 10 preview. I don't have any serious qualms about 8 or 8.1, but I do appreciate the more desktop-centric experience in 10.
Today I tried one of our Java based desktop applications. The process of going to java.com to install the runtime and installing and running our application was as smooth as it is on Windows 7. All good.
My home desktop computer is getting long in the tooth and faulty in the hardware and I've been considering where to go next. If Windows 10 preview wasn't slated to expire potentially a half a year before it's available I would build a new system and put it on today and then purchase the full version when it came out. That six month gap and the potential of needing to drop back to 8 and re-upgrade to 8.1 before upgrading to or purchasing 10 later sidetracks that though.
Impression so far? I'm still lovin' it.