Currently, arduino users are unable to reliably employ baud rates greater than 38400 due to induced bit errors from the UART prescaler system on the AVR. In fact, most users stick to either 19200 or 9600 for everything they do.
This problem can be very simply solved by switching from a 16 MHz crystal to a 14.7456 MHz crystal. Software wise, this would only require a change to the boards.txt file, and perhaps a re-examination of delayMicroseconds (although I doubt it will be much of a change).
Being able to run at 115200 significantly reduces upload time for large projects (I know not truly important, but nice all the same...) and also allows for faster data transfer to and from a PC enabling the creation of more precise data-logging applications.
I currently use my own hardware which runs at this frequency, but it would be nice to have full functionality of the UART available to those among us who may not have the knowledge or experience to create their own custom hardware, or the desire to sift through all of the current derivative offerings.
It would require re-coding and testing of time-dependent code in various libraries. They've currently only been implemented to work with 16MHz and 8MHz.
Most folks who want to change crystals just want to run at 20MHz to get max speed out of the hardware.
Yah; in the interest of "a computer should never get slower", we can note that 18.432 Mhz allows "perfect" bit rates up to 230400bps, and 20MHz allows up to 115200 with acceptable margins...
I woulda been nice if the low-voltage variants had picked 11.0592 MHz or 9.216 MHz, but I suspect that non-serial-related issues dominated. (I see that crystal and resonator selection gets really sparse around there...)
The concern is 115200bps (the default speed for certain Atmel tools like the STK500, BTW.) Although I'm not convinced that the difference between 57600 and 115200 is very important...
