I typically change my fuel filters prior to the snow flying and I never worry about draining the water separator in between changes. Here's a pic of my fuel drained from the separator prior to my filter change. Obviously it appears I'm getting nice and clean fuel.

 

It seems most are finding no water (or just a gew drops) in their separator. I figure I'll drain my when I change the oil or if the light turns on.

 

I checked mine a 2k, just to see what was going on, and no signed of water. Will check it at oil changes from here on out I think.

 

I drained mine at 5K (first oil change) and at 11k (second oil change) and then changed the filters at 16.5K and found the diesel to be totally clean. I do think even with clean fuel, the element will accumulate some amount of moisture and the environment I'm driving in (below zero for most of the rest of the winter) can cause the filter to flow less even if it isn't gel'd or getting an excessive amount of water. I'll change mine right as winter sets in every year regardless of miles.