I have no memory of starting this post, but noticed it so I thought I would chime in. We went ahead and ordered the sink, but don't use it as intended. As several posters have noted, it really is about personal preference and since Campinn gives us the option, we have the best of all worlds.
Generally, we do long hauls. We rarely do a weekend, but occasionally do 30 days or so. Since Keith is a great cook and cooks almost everything from scratch, I think we might use more water than the norm. I also use water bricks and I am in charge of filling and hauling the water. But I can imagine us using it in the future.
We love using the sink for storing liquids on long hauls. E.g. vinegar, olive oil, soy sauce, tamari, laundry detergent, kitchen soap. I pack it in quite nicely and have never had anything break in 1,000's of miles.
The one thing that I would strongly agree with is the Mythbuster comment by Cary. I think the sink doesn't take away any storage space. I agree with AlCat...it gives some different type of storage space.