Yes, I am one of those people that washes Ziplocks! I use them quite often, especially for fresh homemade bread and for freezing food - leftovers, prepared recipe size ingredients, breads and muffins, etc.
Over the years I have refined a system to organize and store these washed Ziplocks so I can keep flavors from mingling and keep foods labeled for freshness.
To start with, the food that goes into the Ziplock is usually in something else like a sandwich baggie. This not only keeps things in usable sizes (so the whole bag doesn't freeze together), but it also cuts down a bit on freezer burn, especially if there is some air space that is hard to work out of the Ziplock. So lets say I dice a bunch of onions to be ready for use in recipes. I will put the diced onions into sandwich baggies, 1/2 cup each. Then these sandwich baggies go into the Ziplock. I know that it would be cheaper to skip the baggies (I don't wash these), but they are quite cheap and I feel their benefit outweighs the cost.

Once I use a Ziplock, I don't switch the type of food that goes in it. This is as much for labeling as it is for freshness. On the label I write the contents of what is going in it and the month and year of the food. When I use everything up from the Ziplock I wash it and put it away. The next time I use it (for the same type of food), I just scribble off the old date and put the new date on.

The way I organize my used Ziplocks has changed a bit. I used to just keep them all together. It got to be hard finding the one I needed since I was getting such a variety of food that I freeze. So now I have them sorted by category in brown paper lunch sacks which are kept in the cupboard. On the bottom of the paper bag I have written what category of Ziplocks are stored in it. When I wash a Ziplock, I just pull out the appropriate brown bag to store it in, and when I need a Ziplock I look in the lunch sack that is labeled for that category.
Now that I type it all out, it sounds a bit complicated. Really, it isn't. I rarely have to buy Ziplocks anymore, and it only takes a second to store and find one. Like I said, the way I do this has changed over the years. I'd love to hear any methods you have.
Maybe for my next post I'll make a list of my categories and what type of things are in them.