Historically the big thing has been the variety of floating point units — nowadays VFP3 is pretty much a de-facto standard on the high-end ARM chips (it's required from Cortex-A8 onwards in the application profile), and what's done on Android (where you have a huge diversity of hardware, some with FPUs, some without) where performance matters is you ship one hardfloat binary and one softfloat binary.
