When someone emails you to ask for copies of some images because they were in an event and they want them for personal use, what do you say? If they wanted prints then I'd charge them print costs but there are no real costs on the web. If they were a band I'd charge them the price of an A4 print as I know they'll be used for promoting their band. But say for a guy who was in a performance, for what I can only assume is to show friends and family or for a record of a great day. Free and watermarked web sized copies?