You might already have this, but here is a link just in case:
https://code.google.com/p/arduino-tiny/downloads/detail?name=arduino-tiny-0100-0015.zip&can=2&q=
Maybe compare feature sets between the datasheets. I've read that at least some (all?) of the attinys don't have built in serial port USARTS so that leaves the hardwareSerial stuff kinda stuck.
I'm curious too as to how much of the library stuff works for the attiny.