The Arduino Wire library for slave mode is very easy.
I'm sure I can find a good library at http://www.avrfreaks.net
for non-Arduino avr chips.
My question was: Is the I2C bus less critical for small timing differences ?
Since some use the internal clock which is not very accurate.
I could also use the UART at 1200 baud, that is slow enough to make it work on every device.
My 433 MHz receiver uses those very cheap receivers from Ebay.
I have a remote control that uses the rc-switch protocol: http://code.google.com/p/rc-switch
That code is even able to determine the pulse length and the codes for any of those.