Wesley has written a report about Linux and the Fossil FX2008 / Abacus AU5005 (WristPDA)(http://www.xs4all.nl/~ernstagn/wristpda/).
The datalink library(http://datalink.fries.net/) allows sending information to the Timex DataLink watches. The original datalink library supports the model 150 and possibly the model 70 watch. This version has been extended to work with the DataLink Ironman Triathlon watch. It has been tested with the Linux SVGAlib output on the Ironman watch only, other output devices and other watches may or may not work, I have no reports either way. The display must be a CRT display (not a LCD).
Jan Merka has written a report about the Timex Data Recorder (Bodylink) and Linux(http://linux.highsphere.net/howtos/timex_dr.php) this device collects information from Timex heart rate and speed+distance sensors (Bodylink System) together with the Timex Ironman Bodylink Performance Monitor sport watch 5E671.
Here is a Linux connectivity HOWTO for the Timex DataLink watch(http://www.vivaolinux.com.br/artigos/verArtigo.php?codigo=4354) (in Spanish. And a video showing the Timex DataLink watch and Linux in interaaction(http://cabelo.linuxdicas.com.br/videos/timex-datalink.mpg).
Linux connectivity to CASIO Wrist Watch Camera(http://www.uni-koblenz.de/~gb/linux/wqvlinkfetch/).
From SlashDot(http://slashdot.org/comments.pl?sid=03/05/21/0046230): "For the gadget happy multitude LAKS(http://www.laks.com/) has made the ultimate wristwatch. It's a USB drive combined with a watch and they've managed to make it look rather nice." This looks like a nice place to store a persistent homedir to use with Knoppix-MiB(http://www.bouissou.net/knoppix-mib/doc-html/Knoppix-Mib.html). See here for another report about Linux and the LAKS Wristwatch(http://www.pixelbeat.org/systems/laks/).
This software provides Linux users with the ability to communicate with the Polar S710 heart rate monitor(http://code.google.com/p/s710/) via the serial IR interface, native IR, and the USB interface. Supported heart rate monitors include the S610, S610i, S625x, S710, S710i, S720, S720i, and the S810. Other heart rate monitors such as the S725X may work to some extent, but this has not been tested. The software comes with a daemon that can receive files explicitly sent from the watch, and a shell-like interface that enables the user to retrieve files from the watch as well as get and set other information. Also included are utilities to convert heart rate monitor data into PNG graphs, print the contents of the data files, merge data files together, and convert them to Polar's HRM format.
See my survey of infrared devices for some information about Linux connectivity to watches.