CrossRoads:
Looks like the ATTiny25/45/85 hardware will support SPI:
Yes it does, but the hardware is different. ATmega 328 has dedicated SPI hardware, ATtiny have USI, which can be configured as SPI (without !SS pin) or i2c. So 328's code for SPI will not work on these.
To code it should not be a problem. Just different port names and setup. My question is how to make the code most portable, so other can use it.