AVR-Chat

I'm considering an ATTiny part but I'm not totally clear on the  
programming and if source level debug is supported.  My reason for the  
ATTiny is the physical size I can have is very constrained.

The programming data line is also the I2C data line.  Does that mean  
no I2C if I want in circuit programming?

Is source level debugging possible on the part?

I'm guessing that I can't have source level debug and I2C at the same  
time since they share a pin.