Chip,
Good stuff! I was brought up in the embedded world back in the 80's and think interrupts vs. polling loops. I've always been surprised how small an RTOS can be to fit into a microprocessor. You really don't need much.
I'm working on a project now that involves a few serial devices (XBee being one) and would love to try it out after I get the initial design in place. Keep up the good work!