I regularly get contacted by people who want to use the art i have here, but are confused by the mutliple licence thing.  For instance:  

I originally described your work as licensed under the CC-BY-3.0, but now I noticed that it is licensed under several other licenses (such as GPL 3). My question: is your work licensed under any of the licenses or all of them together?

I can't understand how can something be licensed under CC-BY-3.0 and GLP3, at the same time.

  It would be helpful for a some of your users if you expanded ""License(s):" on the left hand side of the art entry page to something like: "License(s): choose any"