Recently accidentally dropped my arduino uno on top of 12v battery pack, connecting 12v somewhere to the back side of the board (ground was already connected), killing preinstalled atmega328p, but luckily board itself is intact.
Bought few atmega168p chips in local electronics store (they dont have 328-s, and if i buy it in Internet shop i will have to wait few weeks, thanks to post service..), plugged to my old Duemilanove board, burned Duemilanove bootloader for 168 chip, plugged this chip into uno, selected Duemilanove/168 in IDE, and it works fine.
The main question is - can i use optiboot bootloader with this combination of chip/board? Standard Duemilanove bootloader takes a lot of space, my current project barely fits those 14336B left, and even additional 1000B will be VERY usefull, because i dont need much more space, just 200-300B for debug outputs...
Why not just try it out? If it does not work you can always flash the older bootloader.