Yep, I hate it when I go to someone else's cache and it's way off. A few around here are known to be 60-80 feet off. I didn't want to be one of those people either. For both of my caches I've got out (one is a 4 box multi-cache) I used the method below. (oh, and I use a 60CS as well)
First I stood on site and did an average reading for 150-200 readings (depending on the numbers of mosquitos ). If my dilution of precision was too high, say >15 feet, I'd back out a known direction and distance (yes, I carry a long tape and a compass into the woods when placing caches) until my tree cover was better, lowering my DOP. I'd then do a reading here, as above, and project my actual waypoint the distance and direction to the cache. This helps overcome taking readings under big trees as we often find outselves doing down here.
I always come out the next day or two, and see how close my GPS takes me to my coords. If it brings me back to the right spot, then I use them. If not, I start over as above, and compare results. Do this until you're consistent. That's really about as good as it gets.