Alot of artists are doing some great works on trading cards and mini two x two inch canvases.  I have a very good friend that this is all she works on.  And I was so impressed that I had to try a few myself.  I found out that they are not any quicker than larger works.  But, do cause for some very tight work.  Here is my sample. 

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I suggest that you should try just to see what you can do.  And it provides a great outlet, as well as can get.your creative juices flowing.