I'm lucky enough to be in the closed beta of the upcoming Lego Universe MMO. I've been playing it on a PC at home, since it launched without a Mac client. Recently they did bring it to my platform of choice, and I've been excited to play it on my brand new Mac Mini I have hooked up to a monitor with serious real estate.
I recently patched the game with a new update, and was greeted by this confirmation screen. It seems that the developers, NetDevil, are using a code translation technology called "Cider" to help port the game to the Mac. The developer of the engine, TransGaming, describes the platform as a wrapper for PC API calls that doesn't require the developer to modify the game's source code.
This means that the game isn't running truly natively on the Mac platform. The real questions is whether or not this will cause a performance hit. There is a possibility that Cider could make a similar argument to Wine and claim that the advantages of the platform make up for a potential speed tax that the extra layer causes. Ultimately, the only way to be sure is to play the game extensively on both platforms and run some benchmarks, which is a task I'm more than happy to do.