Thanks for the offer - I've sent you a PM. Is there a bug tracking this so it will be fixed in Arduino IDE 1.1?
I've taken a look at the VirtualWire library and it looks like it is a more advanced interrupt based solution. However, as per this thread apparently VirtualWire can be sensitive to the clock frequency changing with temperature.
I am investigating getting VirtualWire working properly on ATtiny so that I can do a fair comparison.