Picture is worth a thousand words, and video is worth at least 25x 1000 every second

DX 9 vs DX 10 comparison by ATI

Crysis DX9 VS. DX10

Crysis DX9 vs. DX10 - Hunter, Side by Side

Lost Planet DX9 vs DX10

BIOSHOCK DX9 vs DX10

Flight Simulator Vista - comparison DX 9 DX 10

Company of Heroes - DX9 vs. DX10

Call of Juarez Benchmark — Dx9 vs DX 10

Age of Conan DirectX 10 demo

World in Conflict Directx 10 game BETA

As these videos are preety low-res it is best to see DX10 game in action in real life. Go to the nearest computer store and demand a demonstration. Or - ask you friend with DX10 gfx board to show it off…