Ben Gertzfield, VMWare, gave a detailed talk on i18n in their Fusion product at IMUG tonite.
Apparently the VMWare codebase started as a cross-platform Windows/Linux source with #ifdefs and native encodings, and has evolved to support Mac OS X and Unicode.
Some of the issues encountered included raw and USB keyboard support, differing filename Unicode normalization forms, etc.
VMWare is increasingly using ICU, though repackaging the C source only and rebuilding to avoid C++ dependencies.