It all depends what you want out of a gps unit, I use mine to compare my performance and my h.r. over time, If you plan a route a the breadcrumb trial usually works fine, using the right software for the mapping it will give turn by turn, if you go off course just turn round till you pick it up again.
I just have speed, cad, h.r. avg speed, distance, time elapsed or any combination of data that I need for the ride I am doing, mapping doesn't really come into it these days as I know most roads around here, which covers well over 150sq miles, (unless ill and I end up on the A1, even then I just ride till I come a across somewhere I know).
I'm not so sure about that - a smartphone will usually acquire a GPS lock quicker (and can use WiFi/3G to help with this),
This can cause problems with recording times and positional errors, and should in fact be turned off for recording gps tracks to avoid errors.
An old saying comes to mind "The right tool for the job". I wouldn't use a phone for taking pictures so the same is true about gps.