Another GPS alternative
I know this really makes the Geek factor stand out, but another way to get GPS on your bike is with a Pocket PC or Palm handheld. It's pricey of you need to get a Pocket PC or Palm, but if you already have one, you can add a wireless (Bluetooth) GPS unit from DeLorme to your bike and have the Pocket PC or Palm on the handlebars. The nice thing is that you can import or export maps and GPS trails and routes to Delorme's Street Atlas or Topo USA software. More information can be found at:
I have been using this lately to keep track of rides. There are also some landmarks that have been added in such as a house where Charles Lindbergh had to stay back around 1932 when he ran out of gas over a field west of us. If you have Topo USA, you can play back the trail on the map, and it shows the bicycle symbol in 3d as it plays tracks back over the course taken. Street Atlas is handy for planning bike routes too.