Many DSLR shooters are used to 3:2 whether that be APS-C or 35mm full frame. Leaves us Four Thirds owners sometimes perplexed. Sure, the common 4R and the 12R print size is exactly 3:2 ratio. But 3R and 5R isn't. 16:9 movie isn't. Widescreen LCDs for the computer aren't. Neither is A4 paper. Hmmm...

Update: Looks like I'm not quite exact on "6x7 film". We're alluding to the 120 size film (entry in Wikipedia). Although the film was a Kodak initiative, it is now enshrined in ISO 732:2000. This 120 size film allowed various cameras to create different ratioed frames. There was 6x4.5, 6x6, 6x7 and so on.

A long and for the most part interesting thread of square vs rectangular aspect ratios has coincidentally surfaced on the Open Talk DPREVIEW forum. In it, a recitation of the Rolleiflex history occurs.