Well, those who follow this sort of thing knew it was coming. Those who don't won't know what the fuck this is about or why it is important.

http://store.steampowered.com/browse/mac

Steam is now a Mac app and will allow games to be played on the Mac. This is FUCKING HUGE.

The Mac just became a gaming platform that developers will actually consider since there is now a distribution platform for it.

Don't expect changes overnight, but definitely plan on seeing many more Mac games.

I don't nkow yet. I am currently testing an installation of Torchlight. It has steam cloud, so my save games should all be present. It is a 3D game, so it should force OpenGL updates if needed. I'll post how the experience is. Also I'll see if I have any cross platform games that include multi-player components.

If it supports both, you get both.

I had previously purchased Torchlight, Braid, and World of Goo. They all just work on the mac. No re-purchase.

This may not be true for all games, but I think for the most part that is how it works, the Mac is just another client machine.

First hickup.

Steam Cloud between mac and PC on Torchlight is different. They do not conflict, but you can't share your save game. This is specific to JUST this game. Still, I think for older games this type of situation will be common. As games are written for cross platform in the future they will think ahead and avoid this issue.