DirectX to OpenGL in 60 seconds (more or less)...

One of the reasons why PC games get rarely ported over to the Mac and, when they do get posted, arrive after a long wait, is because the vast majority of games for Windows use the DirectX game API, which is Windows-exclusive. Porting a game from DirectX to OpenGL is a major hassle and requires heavy rewriting*.
ATI (or shall we say AMD?) might change the deal [or not]. They offer an open-source tool called HLSL2GLSL (High Level Shader Language To GL Shader Language, Bless you!). It is aimed at easing the transition from DirectX to OpenGL. Of course, it's not a magical trick that will automatically transform your evil DirectX-based code into nice OpenGL goodness, but it should make porting easier.
Let's hope that it will be put to good use and that we will see more games coming to the Mac.
[moose: there have already been a bunch of "DirectX to OpenGL tools for the Mac, but this time it's not some small player releasing the product, but ATI, backed by AMD, so let's hope it's not just hype...]
*[moose: DirectX also offers an API for online gaming, which is why lots of Mac versions of PC games often cannot play online with their Windows counterpart]