Stellar performance via differential 2.5D rendering. This is a dream ;)
This is not in any way to reduce its awesomeness; I just lost 15 minutes I don't have scrolling around and will return to it this weekend! But I wouldn't say it had great performance.
edit: Unless you meant "Stellar Performance" in the artistic sense, i.e. "The figure skater put up a great performance today", in which case wholeheartedly agree :-)
And yes, a more efficient browser version is possible (and possibly simpler). People like to fixate on platforms, but it's all about implementation.