Breaks can get interesting when you have a FIFO'd UART, and a UART error interrupt. I don't recall the CPU but I've seen a situation where the error int happens when the UART is still in the FIFO behind some data.
This caused an issue only with DMX coming from I think a Pharos unit, which sent the break immediately after the last byte of the previous frame.
Haha, it's really serendipitous that you should mention that. The Nuvoton M051 part I just finished testing on last night had this issue. I created a bit of a weird state-machine that sets the FIFO to 1 byte until a framing error happens, and then increases the FIFO to 14 bytes, until it gets halfway through, and then resets it to 1 again. This way I can start receiving at an arbitrary period of time and still use the FIFO.
...of course, once I did all that, I lowered the clock rate to the minimum (which is still pretty high -- it's only a divide-by-16 system divider from a 22 MHz internal oscillator), and the system could easily handle the single-byte reception, thus making the whole thing pointless in this particular application :-)
The wait states in the main busy loop helped a ton with overall power consumption, but didn't change anything at all with or without the FIFO enabled.
I want to go back and use the Renesas RL-78's DMA (yes, a 60-cent 8-bit MCU with DMA!) to see if it changes the power consumption, but at 500 µA, it's currently leading the pack (lots more to review, though, and I've basically only been doing industrial-targetted MCUs that don't have good power figures).
I can't wait to finish testing all the Cortex-M0 MCUs, since the two that I've tested so far — the Freescale/NXP KL03 and the Nuvoton M051 — have vastly different interrupt routine timings with respect to the UART. The KL03 didn't raise an interrupt until halfway through the next byte, and it took about 70% of the byte period to get through the ISR. The Nuvoton part, running at the same frequency, took no time at all — maybe 1/15th of the period. Same core, same interrupt system. Must have vastly different UARTs with different latencies. Totally different power consumption figures, too.