All these gadgets have their niches when it comes to how we use them. For me, I'm more interested in knowing where I am and finding out where I'm going than following a preset route or mapping it afterwards.
I also tend to wander off whatever vague course I set myself to check out interesting-looking sites and buildings. 50K OS maps are ok but 25K ones are great for this because virtually every site of any significance is named.
I could use Google maps or other online free apps just for navigation (or, gasp, a paper map). Google maps in Android 2.1 has turn by turn navigation FOC. They all tend to lack the detail I would like, although there are some apps that give online access to OS 50K maps.
However, the problem with online mapping is that the chunk of Suffolk and Norfolk that I bike round has areas with a poor 2G service, let alone 3G. Online mapping is just not useable in parts of it, so local storage is much more convenient.
Viewranger was surprisingly cheap compared to Memory Map. I selected tiles for all my usual ride areas and it came out to 20 quid so I went a bit mad and got all of East Anglia, London and a large chunk of the South West at 50K scale for £40. The 25K ones are more expensive but still affordable.
John