Who uses Macs for cross-platform development?

By cross platform I essentially mean you can compile to target Windows or Unix (not necessarily both at the same time). I understand that this also has a lot to do with writing portable code, but I am more interested in people's experience with Mac OS X to develop software.

I understand that there are a range of IDEs to choose from, I would probably use Eclipse (I like the GCC toolchain) however Xcode seems to be quite popular. Could it be used as described above? At a pinch I could always virtualise with VirtualBox or VMware Player or parallels to use Visual Studio (or dual boot for that matter). Having said that I am open to any other suggested compilers (with preferably an IDE that uses GCC.)

Also with the range of Macs available, which one would you recommend? I would prefer a laptop (as I already have a desktop) but am unsure of reasonable specifications.

If you are currently using a Mac to do development, I would love to hear what you develop on your Mac and what you like and don't like about it.

I would primarily be developing in C/C++/Java. I am also looking to experiment with Boost and Qt, so I'm interested in hearing about any (potential) compatibility issues.

If you have any other tips I'd love you hear what you have to say.