With the usual caveats of FTA ("You never know what you'll find" and "Past performance is not necessarily indicative of future results"), here's the patterns I've seen:
91 is good for finding local newscaster's feeds. If you like catching live shots from TV channels across the country, they're here. There' also occasional HD sports (often College and High School), or major cable live feeds. I've found live shots from national hosts on CBS and FOX on here as well.
72 seems to have a bit of NBC/MSNBC live shots, or even the rare occasional shot of live hosts on morning shows. I believe this is where I watched MSNBC hosts flip out when Sarah Palin was announced as the VP candidate.
103 will have occasional NBC News feeds, as well as specific promos sent out to local stations (I.e. Brian Williams doing a spot for the evening news mentioning the local news hosts).
79 seems to have the occasional live concert and/or event in HD. I've seen Megadeth, The Met Opera, Prairie Home Companion and more. Also some sports.
123 might be us Ku only-types sole hope of watching sports from Alaska! There's occasional hockey and basketball on here.