I find Memory Map a very useful mapping product, it's support for windows mobile/pocket PC devices and GPS support (on both PC and windows mobile versions) makes it particularly useful for me.
There are quirks in the user interface, but once you get used to them they don't really get in the way much.
The software is in general very stable and bug free.
The only real problems I've had are that to load large region maps (such as this one, the south of England, onto a mobile device, you need to manually split them into smaller chunks. This proceedure is described on the Memory Map website, but one shouldn't really have to do it yourself. Also, if you are short on available memory on your mobile device, you may need to split the maps up even smaller to be able to open them reliably.
One minor issue is that the altitude reported by my GPS is incorrect in memory map (mobile) but correct in other applications. I believe this is something to do with using different models for the shape of the earth. Also, the height profile information stored for producing height profiles without using GPS altitude data doesn't include features such as embankments or cuttings, so height profiles of planned routes along old railway lines (for example) aren't accurate.
Having spent years writing out route cards and trying to protect maps when I go out this package solves the problems. Easy to use, does hours of worth calculations and produces route cards accurately and in fractions of a second, your climb descent and speed parameters can all be changed as appropriate. The ability to zoom in is very kind on old eyes and I can print a new map every trip taking only the bits I need. It's the most used piece of software on my PC.