As for OpenJDK, Apple says that it plans to contribute most of the components required to properly implement Java SE 7 in Mac OS X. That includes "a 32-bit and 64-bit HotSpot-based Java virtual ...

With the OpenJDK project for Mac OS X, Apple will contribute most of the key components, tools and technology required for a Java SE 7 implementation on Mac OS X, including a 32-bit and 64-bit ...

Use a Terminal command to see which programs on your machine are already compiled for 64-bit CPUs.

As a result, in the most recent 2010 Mac Pro systems Apple is changing the default kernel to be 64-bit, and perhaps we will see this be the default for other systems in the future as well.