I can't speak for others either, but the egg crate serves as drainage by way of a false bottom in mine. I also use it for shelving, and for mounted plants, as well. You can see pictures of the setup here:
http://www.orchidboard.com/community...chidarium.html
If you are using it as a false bottom, you don't need the hydroton, really...and vice versa. I like the cleaner look I get with the egg crate, as well as easy access to the water line if it gets too high for drainage. Unlike Ross, I don't clean mine out, though I can certainly see the benefit of doing so. It can get pretty unsightly, though I like the little bits of moss and other freak things I get growing in there after several months. Unless the water is touching the bottom of the pots, I just leave it.