I think there are a few other threads, but I'm not seeing them at the moment. Here's my contexts:
Out the Door
Broadway is a street with several businesses where I do most of my irregular errands. The bank and post office and liquor store are on Broadway. So if I'm going to any one of those places, I might as well go to the rest if I have any reason to. I set the location while I was up there recently.
Home is for anything to be done at home. Laundry, tidying up, doing a photo inventory of all my stuff for insurance purchases, playing Zelda.
Computer is for anything that can be done at either my work computer or my laptop. This is mostly work stuff, but not exclusively.
Laptop is for stuff that actually has to be on my laptop, such as buying an app for my iPhone, or posting photos to my Flickr account.
BugSnacker is for bugs I need to file in Omni's bug-tracking database. I can do these from work easily. But on my laptop I have to connect to work to do it, so it's kind of a pain. And it's faster to do a bunch at once, so I've found it worth separating from all my other computer tasks.
Out the Door is the context I'm supposed to check every time I leave for work in the morning or leave work in the evening. "Take spare iPhone cable to work", "Drop off car for oil change on the way to work", etc.
Phone is completely empty and maybe shouldn't exist. My phone is always with me. On the other hand, I think a "Business Hours" context might be useful for when I need to call my doctor or something.
People is for conversations I need to have. Some could be by email. Some need to be in person. The email ones usually never make it in here, since they're generally less than 2 minute tasks.
Waiting is for stuff I've ordered that's coming in the mail, or anything else thata I'm, um, waiting for. This context is in the "On Hold" state.