Matt-
I've hung several shows myself, frequently in odd spaces that were hard to view the work in (restaurants, etc). On the rare occasion I've been in some kind of formal gallery, usually there the curator/gallery owner does the hanging. I've shown mixed panoramics and standard format images - 8x20 inch prints were framed to 14x24, and 12x18 prints framed to 20x24. I was using some rather large, bold frames (black lacquer wood frames) to make sure the work popped off the wall visually. I aimed for the center line to be at my eye level (I'm 5'10", so around 63"... a bit high, but when you're showing in a restaurant, and the work may be close to where people are sitting, I'd rather go a little higher and avoid having someone's head take down some artwork). I grouped the work: three 8x20s in a horizontal, vertical, horizontal group, then five standard format vertical horizontal vertical horizontal vertical. I tried to keep a minimum of eight inches between each frame. Had the wall been white, I think I would have aimed for a bit more space between the standard format pieces, but the color of the wall provided a greater visual separation (that and we were running out of room on the wall). In a perfect world, I would like to see at least a foot between each frame, and I agree with the notion of doing groupings of three to five, then a bit more space. I would avoid cutesy groupings of images on the wall, however, unless that is part of the point of the exhibit. I find I start wondering about the purpose of the arrangement and not paying attention to the images when things are clustered in a particular formation.