There are two GFX clans. Eclectic Artistry, which I'm a member of, and Live in Colour. Generally, we make small pieces called sigs, what I have underneath my posts. There are competitions between clans every few weeks. Members can also arrange 'callouts' in which two or more members put their pieces against one another, usually making it within a certain theme or using a certain image. Additional rules such as 'the piece must contain a shade of red' are optional.
Some of the members also create larger pieces and they're fairly good at giving feedback on your work. :) (though activity is low atm due to people being busy...but I'm about ;) and it would be interesting to see what you do! :D)