I am not a hardware guy by trade, so I had to learn everything here as I went along (programming in spin, learning how to use I2C, proper wiring (not having pull up resistors set me back a while), and how to use eagle. I still have to finish the pcb and practice a lot more with surface mount soldering before the project is finished.
I first came up with this idea about 2 years ago because my wrist watch was falling apart and I couldn't find any replacements that did all the things I wanted (such as self setting time, compass, solar powered (though that proved to be infeasible given the power requirements for my parts)). I figured that it would be a fun thing to try and build myself, and so far it has, though it has taken my a lot longer than I expected to get this far.
Originally I was going to use radio to sync the time, but those parts were getting harder to find and I already had a spare GPS. At the time I also planned on building a GPS device that would save coordinates from interesting places I had been to (I didn't own a smart phone at the time). It made sense to combine these two project ideas since the watch was going to have a GPS anyway.
The journey from then has been both exciting and maddening. Overall the device works very well and all that really remains is making it fit a watch form factor. Luckily I the propeller comes in a QFP and I have found a smaller GPS unit (about the size of a penny). It may take me 5 or 6 PCBs to get it put together properly (as I've never designed one before) but I look forward to being able to show off the final product.