according to steam only 5% of players have DX11 capable video cards
so that 5% of the people are whining on the forums while the others are enjoying the game
I have a DX11 card, and i have played DX11 games, on Metro 2033, by enabling DX11, i might get better NPC models and some better shadows, but at a 20%-40% framerate drop
so if crytek releases DX11 i hope they do it right with not so much performance drop, or at least a notable improvement
less than 5% actually, I am one of those people on Steam with a DX11 capable card, but I am ok with playing on DX9, it still looks good.