The more forums you are on the more time you spend/waste in front of the computer and therefore not taking pictures or experimenting with your camera which I would think should be your top priority if you want to improve your skills in that area.
There is one BIG one
http://www.redbubble.com but it really is
big and you would need to spend a lot of time and effort to keep things up to date there. I was directed to it a few years back when another forum I was on had to close due to the chap who runs it being in ill health.