Some of you would already be familiar with Ming Thein's blog. He does some excellent real world reviews of m4/3 and Leica gear and IMHO his images and processing are awesome. And we, gear heads do like reviews, don't we?
But Ming Thein also writes some other, potentially, more useful stuff. Recently he's done a primer article on aspect ratios and composition. Well worth a read, I think.
Aspect ratios and compositional theory