In reply to Wee Davie:
When I go out I take the map+compass and an iPhone 4. The iPhone is in a solid battery case and records a GPS track log with Runkeeper. With the battery case this will rind for aboutb11 hours. I do this so I can annotate my photos with the track log when I get home to geotag them all.
I also have 25k OS maps on the iPhone, and the touch panning and zooming beats the pants off any handheld GPS I have seen. However, the screen is to small to be really useful for navigation so I tend to just leave the phone tucked away and recording whilst using my map. On the other hand it's a great way of zooming out for a bigger picture, especially when wind/rain make it inadvisable to take the map out of the case and unfold it. This is particularly great for identifying well distant summits from a top.
It is notable however that the iPhone has never tried to strangle me in high winds unlike the map case...
As things stand a modern phones GPS is accurate to within meters in the hills, and shock proof, waterproof android phones are coming out. Pretty soon the only weak link in the system will be the satellites, and gallileo will help address that. I suspect the statistical odds of a satellite failure are lower than of a map blowing away.
So my take is that a well protected smartphone or GPS is just another tool open for use or misuse. I find it n all round great tool for the hills, and one that compliments the map and compass.