I'd love one, but I can't really afford it and my current graphics card is nowhere near powerful enough to drive one for anything other than 2D desktop performance.
The other problem is that Windows 7 doesn't scale on 4K monitors very well without a lot of fiddling, and I wouldn't foul my PC with Windows 8, so until a stable retail copy of Windows 10 is available (and certified compatible with all the same games as Windows 7) I don't plan on upgrading my OS.
Part of me would probably also want to consider a 21:9 monitor with a 1440p resolution as my next upgrade, as I doubt I'd be able to justify £1000+ worth of graphics cards and monitor any time soon.
Ben