I will start with a negative, that I really only noticed after losing the GPS. It is possible that you will become obsessed by the information that you can get out of the Garmin, measuring gradients, watching avg cadence, observing altitude, checking ETAs etc etc.. rather than just going for a nice bike ride.
My main reason for getting the Garmin was to be able to go for longer rides into unfamiliar countryside, prior to getting the satnav I would tend to stick to routes I knew, even though I love maps and navigation. With the satnav I could plan complex routes on quieter roads and could cut through towns without fear of getting lost. I used this online site to plan all my routes
http://www.routeyou.com/home.en There are lots of sites and route planning software out there but this is the only one I have used I didn't have any problems loading straight to the satnav and would expect most to work easily enough with a Garmin.
example route for one of our local CTC events
http://www.routeyou.com/route/view/126275/cycle-route-tour-of-the-hills-2009.enThe Garmin connect site is excellent and very simple to load your rides to, this is what the route above looks like once you have ridden it
http://connect.garmin.com/activity/11350762?sms_ss=email&at_xt=4d3742b3aa1016e4,0The next thing was discovering that you could record a ride and then save it as a route for the future, this is great if you ride with a group as you can enjoy the company without worrying where you are going and then ride it again solo without any planning. Once you have saved a route you can "race" your self over the same ride, I ended up doing this quite a lot on my commute, your opponent can be shown as a dot on a map or a profile relief view or just as a little animated picture of a bike either ahead or behind depending on how the race is going, great fun as you get to race someone with exactly matched ability to yourself.
I didn't personally have any problems getting the hang of the Garmin but there is a huge amount of things that it can do and the manual is poor, if you do get one and have a problem drop me a line as I can still remember how to get most things setup.
To summarise the 705 was a great training tool, a mind boggling cycle computer, a complete chronicler of all your rides and statistics, an excellent GPS unit and a poor map, the 800 has fixed the poor map so it now has only two downsides, it does cost a lot and it might distract you from just enjoying a bike ride.
