I find that Google Earth along with a mapping software on my iphone does fine. Think the memory map stuff is overpriced
I think you'll find Google Earth doesn't come close to Ordnance Survey for the quality of the mapping. In any case, try using Google Earth or OpenStreetMap somewhere where there's no signal, or data connection. There are plenty of places around where I ride where there's no data available. Doesn't matter how whizzy your mapping 'ware is if you have to rely on non-existent data connections to show the maps. Personally I like to have a nice detailed OS map with the GPS showing me exactly where I am, especially in the middle of a forest, or somewhere out in the open where ROW aren't clearly visible on the ground. I certainly won't argue that MM are damned expensive, and their licencing is pretty restrictive, but at the mo' they are the only OS mapping on the iPhone that allows actual trail recording; Outdoor, sadly, doesn't which is daft. I've got both, but 'cos I don't have a PC, I use MM Free, which gives me 1:1000000, 1:250000 and 1:25k, the first two free, and I can then buy in 700sq Km chunks and just select bits as I need them. Works a treat, and gives me exactly what I've been wanting map-wise since I got my iPhone sixteen months ago. I've actually been using it in the car as a moving road atlas when I've been driving in unfamiliar places, being able to zoom through the layers of detail is excellent. If only they'd be less restrictive on older maps people have paid for.