All was happy and well in x86_64 land until updating my kernel to 2.6.31.12-desktop-2mnb. This is the kernel with support for Virtualbox.
After that, all the 32 bit programs I'd been using just fine would instantly generate a segmentation fault - no other information given, just "Segmentation fault". This includes Skype, ETQW, and Second Life.
Booting to the older kernel (2.6.31.12-desktop-1mnb) makes it all work again. (So glad Mandriva's updater keeps older kernels!)
Anyone know why this is happening, how I might fix it? :unsure: