Steam for Linux has already been released Christmas of 2007!Steam is still coming to Linux with the Source Engine,
Cedega didn't have the best track record for me. I was a subscriber for 8 months, back in the day.
One of the "Gold" games they "supported" (EverQuest) was completely fubared by an expansion about a month or two into my subscription. After that, it was unplayable (unless you just wanted to spend a lot of time looking for your corpse after random crashes or staring at white textures). I filed a bug report, and numerous people complained of the same problems in the official TransGaming forums.
Six months later, not only had nothing been done to address the bugs, but the game was still listed as "Gold" on their list of supported games. That's when I left. I got it working with plain Wine, and it worked fine from then until I quit playing it.
YMMV, but I don't think I'll be checking out GameTree.
IMHO: Native games or GTFO!
(Yes I know that means I won't get a lot of games on Linux in the near future.)
Also, the GOTY 2010 (according to some) is available for Linux (Minecraft).
Transgaming only has a great track record if you ate a lot of leaded paint chips as a child. About the only thing interesting is that developers can use gametree to support their product instead of dealing with the shit storm that is the Linux graphics, audio, and input stacks.
Like Chris Cox's explanation on why Photoshop won't be ported anytime soon: http://forums.adobe.com/message/3231810#3231810
Que someone saying: "Nu uh... Linux is teh bomb!"
Fix the underlying problems and companies might actually port their programs.
I'm sorry, but that's Adobe. You expected anything different? They've got an enormous code base, using a lot of OS resources, which would take years to port to a foreign system. Without a huge market, they're not going to do it. Don't listen to the noise about bad architecture.
Transgaming has their foot in the door already with the worlds largest game publisher, thats a huge deal.