I just grabbed a Libelium GPS shield for my Arduino, and wanted to make it work. With minimal effort (about 20 minutes), I was able to get a fully functional GPS system working - incredible. Pardon my enthusiasm, but rapid design and prototyping like this was never possible when I was in school. We were too busy making LED's blink back and forth ala nightrider - and for the adventurous - debounced button inputs ala simon. Fastforward to 2007, and you can have a fully functioning GPS-enabled accelerometer hiking / backpacking logging device in less than an hour of mixing parts together.
Without further ado, here's a picture of the GPS shield sitting on my Arduino:
I'd go into further detail about the circuit or the schematic, but there's really nothing to talk about. You just pull the board out of its wrapper, snap on the antenna, plug in +5V (red wire) to the pin tower labels "+5" and ground (black) to the pin tower labeled "GND". Set the board starting at the Arduino's pin number 8, and you're set to go.
As usual, I've posted the source code for the project over at liquidware - enjoy!