I was given a project for a client to design a PCB, using components he had 'laying around', this included attiny85s, atmega328s, relays, and a box full of passives. (He was looking for a board he could sell to end builders that needed minimal extra parts to build a working Arduino based control board - my final design will be 100mm x 80mm). I looked at installing a V-USB Bootloader on to a 328, but 1/4 watt 3.3 Volt zener diodes (needed for clamping the voltage to USB Spec) are not an every day component. Then I saw AVR-CDC for the ATTINY series of chips, I built one based on the 85, but the limit was 4800 BAUD. I Then looked around for a bootloader capable of running at this speed. I Could not find one, but I found a close match in a IR Based bootloader running at 2400 BAUD. Looking at the code, it was not too difficult to change the BAUD rate. changed it to 4800, built&uploaded the bootloader, it at worked . . kind of. It would work about 1 in 20 times ! ! ! ! ! ! Thinking it was a % error (look it up) I changed it to 4740 (Through trial & Error) and it now works 9 times out of 10 (occasionally it will not verify - but next upload does)
I've included the bootloader files in this post - the AVR-CDC link is http://www.recursion.jp/avrcdc/cdc-232.html
Hope this helps / inspires.