I just wrote a comment on DirectX 11 powered Dirt 2 video showing off the new DirectX features. I thought I blog this too.
 
DirectX11 is not a major leap forward like DirectX 10 (or previously 6, 7 and 9) have been, as all of you in this thread already know. 11 is a nice upgrade for 10 on the rendering side. Sound, etc ... no major changes as far as I see.
 
And here a summary of questions people might have, who are not familiar with DirectX (old Dudes, look away;)

• You need a DirectX 11 videocard for your PC to run DirectX 11 effects on the hardware. DirectX 10 or 10.1 chips won't do the trick.
  
• DirectX 11 is not supported by your XBOX360 - neither by a PS3 or Wii or your TV (seriously, don't laugh. I get those questions)
• You need Windows Vista or Windows 7 (not backwards compatible with XP or older OS versions!)
  
• You don't really need it. There are some nice cinematic effects as you see, but everybody can live without them and many new games will in fact be without them. The multi-threading features are supported already - yet not that many games are really using multi-threading to it's full advantage (because it's 1. hard as hell to programm and 2. limited by videogame design issues in general).
  
• Hardware Tessellation is something you have since the first AGP-graphics cards. Messiah was to my knowledge the first game that shipped offering this feature to gamers. (I could be wrong).