I've standardized on a few ratios, because otherwise printing and framing them is just too much of a hassle. My favorite ratio is 2.5:1, this seems most natural for my compositional style, and I find it a pleasing ratio (maybe due in part to watching so many movies that are 2.4:1 widescreen). I also use 3:1 when it fits the composition. Every once in a while I'll use 2:1 but that's not even really a pano to me.
I don't care for ultra-long panos. 3:1 is my limit, as I find that anything wider than that and there really doesn't seem to be a composition. (fike's comment about a 'thin ribbon' is spot-on IMHO). Sometimes I see these uber-long panos of mountain ranges or city skylines that have ratios like 8:1 and to me they're just boring (no offense to anybody who like that kind of image, they're just not my cup 'o tea).