Hi,
as discussed in an another topic, it seems designs with the 1284p may benefit when Full Swing Oscillator setting has been used, at least as the upload reliability is concerned. The 1284p DIL has got flipped XTAL1 and XTAL2 pins against ie. 328p, thus the 1284p' pin XTAL1 (crystal oscillator input, sensitive, high impedance) could be affected by the noise injected from adjacent pins (ie RX0).
http://arduino.cc/forum/index.php/topic,139671.120.html