Early Garmin units were frustrating (i3, 600 series nuvi [?] with Enterprise rentals), took to long to "recalculate" to be useful due to sluggish processors, best GPS feature to me is to get back on track or re-route when you miss a turn, especially as you zero in on a never-before-visited location.
Sprint Telenav was unacceptable due to long delays in calculating directions (until after you've missed your turn) due to delays in retrieving data from satellite (Sprint issue?) as well as audio commands being way too low in volume, especially at highway speeds (couldn't listen to radio and GPS at the same time).
Currently I am loving the nuvi 760, which has been a dream that has taken some of the bitterness out of the urban experience for me, which as some may know is not one of my loves.
Fast satellite acquisition as well as fast recalculation are extremely useful in a medium to large city (so far have used in Dallas as well as LA area, which seemed more like a medium sized neighborhood rather than a sprawling metropolis), traffic data can also be essential to anticipate and/or avoid bottlenecks/traffic jams and to find smooth alternative routes.
Preliminary word from CES 2009 has it that the nuvi 885T is even better, with accurate response to voice commands (already road tested with the 800 series) as well as graphical lane change guidance.
GPS units clearly are ready for prime time, and affordable as well.
