Actually no, I did run BeOS PE5 for about 3 months as my main OS... But while I did like some of the ideas behind it, I was never grabbed.
The Genode thing you linked me to, look much more interesting.
BTW, I like darwin for a few reasons: it is built for x86 and ARM (my two hobby CPUs), it's a microkernel (well more a hybrid) and it has a fully featured Obj-C runtime that suits my predilection for Obj-C at the moment 
The BeOS API is a thing of beauty, it is the hardest of hardcore pr0n for the C++ aficionado!
