disadvantages to higher baud rates?

Are there any disadvantages on the Arduino side to choosing a higher rather than lower baud rate for the argument to Serial.begin() (or, for that matter, choosing the highest possible baud rate that the hardware supports)?

In my case, I'm less concerned about receiving data into the Arduino and more concerned about sending data. Thanks in advance for any help.

When transmitting serial from an Arduino it is always better to do so (highest rate possible) IF the receiving device or PC can keep up with the data rate. That leaves more time avalible for your sketch to keep processing other tasks. This is not as important in version 1.0 of the Arduino IDE as now the serial library uses interrupt driven serial on both sending and receiving where as prior version used interrupts on only receive. So slow baudrate transmitting does not have the negative impact it once did on the arduino sketch as long as your serial messages being sent are smaller then the transmit buffer size used in the serial library. If messages are longer then the buffer size then the transmitter characters do become 'blocking' commands and can slow down normal sketch processing.

Thanks a lot. That's exactly what I needed to know.

In the case of a full buffer, is there a way to calculate the approximate amount of time per byte in microseconds during which transmission will block, as a function of the baud rate and perhaps values from the device's datasheet? Or does that also depend on characteristics of the receiving device (PC in this case)?

baudrate is bits per second, the overhead is a start and stop bit and some time between bytes. Total time for 1 byte = 8 bits + start + stop + 1 = approx 11 bits.

So if you divide the baudrate by 11 you get a reasonable estimation of the maximum effective transferrate. E.g. 230400 baud => 20 K bytes per second 115200 baud => 10 K bytes per second 9600 baud => 870 bytes per second 1200 baud => 110 bytes per second