4K Personal experience post time.
I bought myself a 4K monitor (this one from Dell: http://www.pccasegear.com/index.php?...ducts_id=30305), and the quality and clarity is absolutely stunning. The high resolution is also extremely useful with some types of programs (eg. Gimp, Photoshop, Illustrator, Maya, 3ds Max).
With games, the improvement depends on what you're playing (in my opinion); I prefer 1080p for most strategy and mobo games (eg. Europa Universalis, Civ5, League of Legends) (I think some might like it for Total War because it focuses more on pretty graphics than most others in its genre, but I still use 1080p on TW anyway). 4k is definitely best on FPS and RPG games (eg. Battlefield, Skyrim, GTA, Bioshock, Farcry, Assassin's Creed), but the amount of PC power needed to run games like this at 4K & high settings is definitely too much, so not a realistic option at this time.
Windows 8 generally scales the UI well most the time for programs, but sometimes it doesn't, and it breaks the experience eg. Photoshop is unusable for me at 4K on Windows 8 because the UI doesn't scale at all (same with other Adobe programs, and Gimp) and I get minuscule buttons. So if you want to use Adobe professional programs like this and want a 4K monitor, either wait for Windows 10 (which will have a much better API for UI for scaling), or run it on Mac OS X (which has had great UI scaling for Adobe programs for a long time; this is what I do).
Also, Windows does a terrible job at scaling the UI for a multi-monitor setup, where both monitor have different resolutions. I have my 2650x1080 monitor (not a typo, it's a ultra wide ) and 3840x2160 connected at the same time, and the text will be annoyingly blurry on whatever monitor I set as my secondary. Sounds like a small deal, but when you spend $500 on each monitor, it's definitely not (don't scald me for spending this much, I actually need it for what I do )
All in all, I don't think 4K is worth it at this time. The industry isn't ready for it, and we're still waiting for plenty of the massive companies to properly support it in their products. By the time 4K is supported properly (probably not too long after Windows 10 is out), and graphics cards are better geared for these higher resolution screens (higher memory bandwidth, higher VRAM capacity), 4K monitors would have decreased significantly in price.
Owww... that'd hurt :/ Have you done much searching as to why this is?