Interrupts have not been supported by my first release. I created a new release today:
- added Interrupt support for INT0 and INT1.
So you can use
http://www.arduino.cc/en/Reference/AttachInterrupt
just like on the official Arduino.
The Wire Library compiles without problems. So I2C is available. But the example sketch is too big for the small memory of the attiny2313. So I think that I2C can be used, but you must modify the Wire lib... I can do that for you if you don't know how to do it. The Wire lib can be split into two parts: master and slave... so if you want the tiny2313 to be a I2C slave, then you don't need all the master routines in the memory (because they won't be used in this case)...
I also included this fix to Print.h and Print.cpp:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1244128096/0#0