I am very interested in this, and I bet many here might also be interested:

http://www.ecnmag.com/Products/2009/11/Sports-Watch-Development-Kit-Fits-on-your-Wrist/

It's essentially a watch with a wireless capable MSP430 processor, 3
axis accelerometer, pressure sensor, and temperature sensor.  Kit
includes the watch itself, USB jtag/ice adaptor, USB wireless dongle,
software, and a tool to dissassemble the watch.

The entire kit is only $49.

Wiki:

http://wiki.msp430.com/index.php/EZ430-Chronos

TI link:

http://focus.ti.com/docs/toolsw/folders/print/ez430-chronos.html

It's a sub 1GHz radio, though, so no zigbee or ANT, but apparently
another company already has compatible heart rate monitors, and they
plan on having wireless bicycle sensors available next year.

The example software (pre-programmed) includes the usual
time/date/alarm/stopwatch functions, as well as altitude, temperature,
pedometer, and wireless PC control (powerpoint presentation
controller, for instance, or accelerometer controlled mouse).

The LCD is limited to 96 segments - looks like four 7-segment digits
(88:88), a bunch of indicators, then five point five 7-segment digits
(18:88:88).

The chip it's based on is a pretty spiffy SoC (
http://focus.ti.com/docs/prod/folders/print/cc430f6137.html )
including the radio, lcd driver, 16 bit mcu, 32k flash, 4k ram, and
AES-128 cryptography coprocessor.  Not cheap, but probably on par with
a separate MCU and radio combination.

I havent done MSP430 in a few years, but it's very tempting to get one
just as a toy.  Too much stuff on my back burner already though...
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