I've just released beta 2 of picoboot. There are no changes to the bootloader code - just to picoboot-avrdude.
Instead of erasing as pages were written, it now implements chip erase, erasing the page before the bootloader down to page 0.
With the previous programming algorithm, if power was lost between erasing and writing page 0, the bootloader function could be corrupted. Now when page 0 is erased, the rest of the pages up to the bootloader will be erased too. Erased pages are set to 0xFF, which acts like a nop, so the avr will run through the empty pages until it reaches the bootloader code.
Source and link to Windows & Linux binaries:
avrdude -p t84 -c picoboot -P com16 -U flash:w:../avr/t84tTx.hex drain>