We're also trying to apply patches to the Arduino core that would make it portable across processors. Mark Sproul has written a bunch of them that Christian Maglie is helping me integrate. See: GitHub - cmaglie/Arduino: open-source electronics prototyping platform. If anyone can try these on the ATtiny45 and 84, that would be great. Eventually, we'd like to make it so you only have to write a single file (e.g. pins_arduino.c) to port the core to another processor.