OpenGL & DirectX

Alright, so this isn't a "which one is better" thread. I've been experimenting with both and kinda go back and forth between liking the two. DirectX I don't personally like (atm at least) cause you have too set up Vertex buffers and shit from the very start which isn't exactly useful when you're just trying to hack program something together.

Anyways my question is what reason(s) do you guys have for using either one for your programs?

>>1
OpenGL implementation availability: Windows, Linux, Mac, various UNIX, Android, other mobile devices, Nintendo consoles I think, HTML5 web browsers, other stuff I haven't heard of, ...
OpenGL programming availability: Anything from C to Python to Racket.

Direct3D implementation availability: Microsoft.
Direct3D programming availability: Microsoft.

>>9
nVidia OpenGL drivers are working fine on Linux.

>>10
If your graphics card happens to be an nVidia one, and your operating system is Linux, the driver is pretty good quality, stable and fast as well. nVidia's Linux one is a quality driver, I can tell by some of the programs I run and from having seen quite a lot of shitty drivers in my time.