Here's an idea for free. Someone should setup a photo-printing site with an Open API which all the thousands of free image sharing sites
could use to get their images printed. The printing site would pay commissions to the sharing sites and would handle all the billing etc.
(Paying commissions is pretty normal for photo printing sites – some pay up to 25% of an order, but all require the user to manually upload the pictures to their site.)
It's a win for everyone – if you want to build the next FlickR you would have a potential income stream. If you are a consumer you get to choose the best sharing site, and
finally if the printer operator wins because of increased number of orders coming though from the affiliate sites.
SmugMug has (AFAIK) the closest I've seen to an implementation of this idea. They have an upload API and printing
capabilities, but it is primarly a photo sharing site which you need to join to get pictures printed.