I've used both the USBtiny and a cheap $5 Asian E-bay usbasp programmer to burn bootloaders and sketches to both 644P and 1284P chips. It always works but the USBtiny often reports a verify error upon completion but it appears to be a 'false positive' as the resulting bootloader and fuses always end up being fine. The USBasp has never reported an error. And I'm pretty sure I even used a arduino board running the arduinoISP sketch to burn a bootloader to a 1284P with no problems seen.
Lefty