I'm guessing with the Garmin 60csx you'll probably have enough memory on a 2G card to store all the lakes in the US PLUS all your points you mark. None of that grabbing a different card for each lake. Again, I don't know how detailed the lake maps are. I'm betting the H2O has better detail but if you also want to use it for hunting, the Garmin would probably be the way to go.
One issue with the Garmin 60csx is you have to buy the unit plus the maps you want. Right now, I only have the base map that comes with the unit but I'll eventually get lake maps, topo maps and street maps. Each set of maps is about 100 extra. When you get the street maps, it will give you driving directions, which is cool. If all you want to do is mark waypoints and not get lost, you don't need any extra maps.
I used it this past weekend for a geocaching hike that took me about 5 miles along trails I don't know. It was easy to follow the gps track back to the starting point. Without it, I'd probably still be out there!
Try searching this site for more information...
GPS INFO
_________________________
Lone Star Carp Brigade - Dedicated to the promotion, education and camaraderie of carp anglers in the great state of Texas
PB Smallmouth Buffalo 65lbs 2ozs
PB Mirror 34lbs 4ozs
Big Carp Tackle