I have not used "memory Maps"--I am also not clear on their pricing policy--and how often you need to pay up upgrade. Also I don't see Active Captain, which is a great aid in any mapping program.
There are a number of other programs which provide free or minimal marine charts or Topo maps. Topo maps are good for Powell (or other lakes which fluctuate,), since you are not dependent on someone's idea of where the water level is (often depicted at full pool, which is rarely the case.
I have been fooling around with Skipper recently--which has multiple type of maps, NOAA, Topo, satellite, road, history etc. And is about $12 a year for all of the upgrades. It seems to be the only one which has Active Captain on Powell, and I am going to put some of my favorite places on the charts. With Topo it is fairly easy to ID where you were at what pool level.