I made the upgrade, it's really not all that bad. The process was pretty smooth, most of the time necessary is just for the download. Everything is where it was before and still worked. Only thing worth knowing is you should deactivate certain programs like Maya/3ds Max and zBrush first, so they don't see the new OS as a new computer. Took me 5 mins to deactivate/reactivate them afterwards. Otherwise the only issue I've had is GTA V doesn't run so well, it crashes after awhile (I think it's the Rockstar Social Club, crappy DRM) all my other games work though. With the inclusion of DirectX 12 and fully supported games coming soon, support for XBOne wireless controller (after the adapter comes out), and the fact that it's a totally free upgrade there's really no reason not to.
The privacy issues people are going on about are customizable, you can switch these things off. Ultimately it'll work about as well as Win7 with an interface somewhere between 7 and 8.