Some discussion about default baud rates with reference to esp-open-rtos got me curious so I spent some time poking around with the baud rates:
Documentation & speculation here:
http://esp8266-re.foogod.com/wiki/Serial_UART
UART seems like a good candidate to figure out how the PLL clocking actually works, so I'm hoping to try some more of that soon unless someone else gets there first.
Angus