This clever device gets an A+ for its potential and a C- for its execution of that potential. I've been using the Garmin Edge 305 for nearly 3 years now and while I love the data that it gathers and the convenience of swapping it from bike to bike with no wires, magnets, or other accessories, I'm continually disappointed by the software Garmin developed to accompany it and the limitation of 7-9 hours of battery life.
Normally those problems are minor since I can charge it after a long ride and download regularly to my PC (not my mac because I don't have the newest, Garmin compatible OS on the mac). On my cross country journey however I had to scrape around for power outlets every time I stopped to be sure I got a charge. Also, I was not initially aware of this but apparently the device will overwrite historic data as it gets full. And it gets full after 10-12 days of long rides. Without a personal computer on my trip and unable to upload activity at the numerous libraries I stopped into, I learned when I finally got home that the fun stuff like elevation gain, daily route maps, calories, and max speed were overwritten for the first 3/4 of my trip. Total bummer because I was looking forward to sharing those trip totals.
Maybe someone out there has created a better software solution than the junk that comes from Garmin. I've played with sportracks and while it is better, it still has some major limitations. Linking with google earth is fun and allows you to see the topography and satellite pictures fo the terrain that was covered but it doesn't do anything to help store a route without having to first download software onto a computer (which you cannot do at most poublic libraries).
Anyway, I'll continue to use the Garmin Edge 305 and be satisfied with its abilities as long as I am near a personal computer to sync the data regularly. When traveling for extended periods though, an old fashioned wired computer is still going to be necessary.