I'm currently running Mac OS X 10.3.3 (up to date as of May 14, 2004) and note that, although OS X comes with gcc, gcj is nowhere to be found. My guess as to the reason is that maybe Sun doesn't want Apple distributing gcj alongside the JVM... Sun really likes their "write once run anywhere".
So, does anyone expect to see gcj on OS X any time soon? I'd really like to see Apple start contributing code to gcj... Personally, I see ahead-of-time compiled Java as the way to go. Fast start-up times, low memory use. Just like C++, but without the C++. ;)