MacOS X offers a great Java Development platform. It comes bundled and works pretty much the way it should. Installing the eclipse IDE is a simple download and drag n' drop affair.
The default comes with Java 1.4.2 with Java 5.0 downloadable via Apple's developer site. Performance on the 1.33ghz ppc is comparable to my previous Centrino 1.6ghz x86 machine. The difference tho is the somewhat distinct creativity inducing allure generated by the general combination of slick hardware and drop dead gorgeous software. Truly inspiring.