Part of my photograph has been studying/evaluating the great photographers of yesterday and today. Many great landscape photos have been made in 4:5, 3:2, and 3:1 aspect ratios. Cinema generally used, IIRC, a 2.4:1 ratio (something you notice in IMAX movies like the recent Batman movies, which combine 3:2 Imax as well as 2.4:1) Previously, aspect rations were dictated by film aspect ratios, though I suppose people could crop if they wanted to. Digital allows us to make variant aspect ratios quite easily.
However, it seems that 16:9 is becoming an increasingly standard ratio. Beyond display on HDTVs (not as critical for stills as it is for video), many monitors are moving to 16:9, the current Samsung Galaxy and Galaxy Note* are 720p (i.e. 16:9). The next iPhone is rumored to be 16:9, and I wonder if many future platforms will migrate there.
Does anyone shoot or process still landscape photos with a 16:9 output in mind? Of course, we should match aspect ratio to subject, but I've started experimenting with 16:9 and while I've long preferred 3:! or 4:5 I'm beginning to like it.
* as an aside, I'm seeing a lot of these in Asia these days and they are really, really cool. Looks thin, fits in women's purse very easily (VERY important marketing decision), lighter/more portable than an iPad, and IMO the perfect size for ebook reading or TV/movie watching (Korean cell phones have HDTV reception capability). If I wasn't a US Verizon subscriber I would consider dumping my iPhone for one, though I think the iPhone's experience/interface is better than Samsung. And yes, I do mean Samsung and its Android "skin", not Android.