I think it's more than fair to ask someone to come in for a couple of hours and see how they work. How is it any different from companies that sit you down and give you tests that can go on for hours unpaid anyway? Think of it as an interview, two hours is not unreasonable unless you're afraid you won't be good enough.

Once again some people on HN take things to heart way too easily. You can't voice an opinion on something without someone taking it the wrong way or personally.