Just browsed at viewranger, tried the demo on my N96 when it came out and played with it on a ride with a chap who was testing it for a mag on a Nokia 5800. Was pretty good and looks like it's been improved, I may well just think about that now.

If you already have the Viewranger maps on the DVD from a Nokia then you can get the iPhone app and copy the maps across via wifi, then you can add more maps to what you have, like 1:25k in 700 sq km bundles. Things like the panorama view are being added in future updates. I've got Memory Map Free, which has just had an accuracy update added, and which works fine in thick woodland, and which will work with the lock screen on. You just turn on the iPod, then pause the track, and go into MM, start tracking then you can lock the screen. I was tracking a walk in woods near Marlborough, and several times went out of MM, took photos then went back to MM and it carried on logging the walk. 3.42 miles in total.
When I get my new 4G next month I'll be able to install my Viewranger maps, and UK Map, Phil Endacott's neat app that gives an OS base map, and free 5k tiles of 1:10k OS maps.

Aye tempted by viewranger might take a look today.

Gone for it this am and you get a lot of 1:25,000 in with that price so well worth it, added the most common ones I ride on and a few around the Lakes. Have about 10 tiles left so some careful choosing now but £10 for more tiles is a good price too.