I have used the nokia 5800 with viewranger (1:50000 whole counrty and 1:2500 lakes)for about 12 months now and have been very impressed. As a hill walking tool I have found it very useful especially when navigating in fog and it is just so much quicker than frequently consulting map and compass. It must save a good 1/2 hour when navigating in bad weather.
A few user tips though :- the battery will last 7 or 8 hours but if you need even more then press the phones 'on' button briefly and select 'offline'. This will turn the phone reception off and stop the battery being used to contunually search for a network. This means no-one can call you on the hills (not a bad thing) but you can easily switch back online if you need to make a call.
Another useful tip is to use a protective cover. I use the Boxit case http://www.boxit.net/ which is waterproof and shock proof. You will need to turn off the phones automatic keyguard as the unlock slider on the phone is inaccessible with the boxit cover on. To wake the phone up you then simply touch the screen. With the cover on it requires a slightly harder press than usual to register but this prevents the screen unlocking by accident in your pocket.
This now essentially eliminates the main critisism of this system by making it a durable as a purpose made outdoor GPS device.
Overall a great piece of kit which I can highly recommend.
(Written by: stevepne)