I would guess there's a difference in speed and maybe a few features, but not as many major games are made with opengl as there used to be. I'm guessing that opengl 3.0 would be more useful for people in 3d design.
But I have absolutely no idea, that's just my guess.
3.0 mainly cleans out the API. Really, only a few major games use OpenGL (Doom3 does, and Doom4 will). A lot of independent programs use the OpenGL API though...