Online photo sharing site 500px has launched a special offer in conjunction with Klout.
Using your Klout “score” you can either signup or upgrade your 500px account and get a discount.
The offer was launched several months ago, but I only came across it today! (thanks to Paul)
Bottom line – the higher your Klout score the bigger the discount. You can get anything from a 10% to 100% discount
Full details here.