I love my 305. I love the maps it makes, and that I can track my speed and heart rate.
Using Ascent software for the Mac makes it worthwhile. Without Ascent I wouldn't lik eit nearly as much.
Ascent also sends the data to Googlr earth and you can play back your ride as a fly through. No training value, but big fun!
I'd like a 705 for navigation, but they are too flippin' much for me right now. But you need one.