Hey Jack,
It is running fine under Linux x86_64 right now, with just a couple of minor issues that I'm ironing out. I have to rebuild the entire platform for Win64, and we'll have the first 64-bit versions of PixInsight ready for release. If no further problems arise, this should happen during the next week.
Along with the fact that 64-bit applications are much better adapted to modern hardware, I am using now the latest development tool versions: MS Visual Studio 2008 on Windows and GCC 4.3.0 on Linux. This will produce more optimized code on both platforms, for both the 32-bit and 64-bit versions.
Time to step forward 8)