Accuracy is definitely the part that has stopped me from converting totally. A couple of months back just after getting a new phone, I took both the phone and my GPSr with me when I went to do a few caches around Shurdington. I kept firing up the GPSr to check I was in the correct place that my phone was telling me I was, some of the time I was, but for one cache the phone put me over 50' away from the cache. The GPSr took me right to the correct spot.
I know there is much more to it than that, and it depends what quality of device the hider used, and other factors. But I still have a deep down feeling of trust that my GPSr is putting me in the right spot.