Buying a gps unit based on the fact that you own extra SD memory cards is kinda like choosing to buy a car because you happen to have a set of tires in the garage that will fit it.
As in the car analogy, there are many more important features to consider other than memory format. I would rank features such as sensitivity, available maps, battery life, screen readability, support, etc. as more important in the long run.
Also, if you buy something like a Garmin 60CX for around $400, a 256MB micro-sd card that costs only $20 represents about 5% of the cost of the unit. Purchase a couple of mapping packages and the percentage cost drops further. And you can fit a lot of maps on a 256MB card!
