Alas, Picnik is closing as of mid-April ... I'm sad!! They've refunded Premium membership costs (a mere $39.95/yr) and are going on to other things. I loved Picnik, and now I must find a new home to do the same/similar stuff.
I'm trying out two sites I've found. One is called PicMonkey (seems to be a natural for a CardMonkey, ehhh?). I created this photo (enhancements) using this so-far-free program ... the site seems to be the closest to Picnik that I've found ...
The other site I've found is called Aviary. I haven't played around much with this site (yet) but it seems to have far-reaching techniques to enhance all sorts of media. Maybe more to learn initially, but definitely has cool effects that are possible. I played around a little bit with one of their stock images, and came up with this "Raining Rainbows":
Have you tried any other online software programs to edit your photos? I'm hunting now, and would appreciate any suggestions!