...lol. WTF. Yes, it is used. It's a newer tech but it's used already in AVP, STALKER: CoP, Dirt 2, BF:BC2, Metro 2033, and Battleforge and it is going to be in another 9 upcoming games soon, and any new games will definitely be picking it up since it's the new *** and is supported by ATI and Nvidia.
http://en.wikipedia.org/wiki/List_of_games_with_DirectX_11_support
Also:
http://forums.gamespy.com/computer_hardware/b50692/19944893/p1/
Features of DX11 include:
1. Uses much less system memory irregardless of how many windows you have open. However GPU memory will still be consumed (so close them windows before playing games)
2. Introduces Direct2D for hardware accelerated 2D. This is a replacement for the software only GDI/GDI+ Windows uses to render 2D objects (like splines). Direct2D is rumored to be ported to Vista and XP.
3. Better display scaling, this is mostly when you have a projector hooked up to your widescreen laptop.
4. Most of the DX11 features are compatible with DX10 hardware.
5. Multithreading support. This means DX11 functions will support multi-core processors.
6. Tessellation - This takes a polygon and breaks it up into even more polygons. This allows for smoother looking curves and higher detail. The best way to think of this, it's as if you took bump mapping or virtual displacement mapping but it's actually real polygons instead of texture tricks. This is the only feature that requires DX11 hardware.
7. Better GPGPU support, if you're into that thing
8. Heterogeneous graphics support - This was missing in Vista but was in XP. Basically you can take two different graphics cards with totally different drivers and have them run at once. But this isn't an alternative to SLI or Crossfire. Meaning if you run a game, it'll still run on one card or the other.
Anyway, the 4890 does perform better, around 5 fps better average or thereabouts. So if that's all you care about then it's a good choice.