Hey guys... I thought to ask around on Bookcrossing and a few of them put their photos on here. They told me that there's a Flickr group for Picnik people who loved the site and were devastated it was shutting down; so they got together and shared which editing sites they used. One of the most popular - and the one that was most like Picnik in every way - was iPiccy.com. I tried it out and it is so much like Picnik in all ways I could have sworn it was a distant cousin... have a go... you will enjoy it. :)
