I think it boils down to what you feel you 'owe' to someone who's items you've used in your pictures. I generally credit anyone who's freestuff I use, because I consider it 'payback' for their generosity in sharing, not because they helped me create my pics. As for items, I've purchased.... I almost never give credit unless I am majorly impressed with the product. After all he/she got their pat on the back when I punched in my credit card number.