Vista's compatibility issues are, for the most part, resolved.
Probably the most notable game that utilizes DX10 graphics (other than the recently released Crysis) is Bioshock.
The most notable part about DX10 is the new particle effect that makes airborne particles look and react to the environment more realistic. This is noticeable with dust clouds and rays of light that pass through a dusty environment.
Another notable feature is the water effects and how water reacts to it's environment. Rather than seeing pre-made animations, the water will realistically splash and ripple accordingly to it's cause. This, however, can be undermined when a game already has realistic looking water effects.
Supposedly, DX10 is suppose to make shadows look more realistic but, otherwise, it takes existing shadows and dithers(wording?) the edges. Many games are already able to do this under DX9 but DX10 may take up less resources doing this.
DX10, supposedly, is suppose to take up less resources rendering graphics than it would with the same graphics under DX9 but this is probably highly debatable.
The last thing that can be notable is the new shader capabilities, making textures look and respond to the environment more realistic. Probably the most notable textures would be the reflective metallic or fur. This too can be undermined if the game was already made with realistic looking textures under DX9.
The best thing to do is look up DX9 vs DX10 shaders and graphics and judge for yourself whether it's worth it. You need to be careful though because some screenshots of Bioshock, under it's DX9 shaders option, will use a hybrid of DX9 and 10 shaders and graphics.
