I have a number of Arduino Pro Minis with Atmega328 in two flavours: 3.3V @8MHz and 5V @16MHz.
Upgrading the 5V Pro Minis to Optiboot via AVR ISP MkII has worked nice, maybe with the small flaw that the Optiboot board options want them to be selected as Duemilanoves. Nothing serious, as the specifications are basically the same and things seem to work alright.
However, when a 3.3V Pro Mini is upgraded with Optiboot, it won't accept any sketches through the Arduino IDE anymore. Some blinkage of the TX LED on the FTDI board, then timeout. If I go back to the non-Optiboot loader, it programs fine again. I have reproduced this multiple times, back and forth, with two 3.3V Pro Minis. (I only have one FTDI board, though.)
Any suggestions on this? Have I hit a bug in Optiboot?