Honestly, I think cameos are part of what made early Marvel comics so much fun--yeah, they boosted sales and the like, but a quick guest shot by Hulk in the FF was a must have kind of thing.
In that spirit I think they could be great fun--with permission to use them of course.
Yeah, cameos are kinda fun. I'm good with 'em.
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I like it. And I totally wouldn't sue.
Thumbs up for cameos with permission. 
A lot of us already use cameos, Slick. Just obtain permission from the owners, first. The owners might have questions about how their characters will be used, of course, you probably already have an appropriate use in mind, so it shouldn't be difficult to explain the situation and still get permission.
My Stories
Look at that. A full-grown woman pulling off pigtails. Her crazy is off the charts.
The "use" I'm talking about is sort of like if a scene took place in a post office and a "Most Wanted" list happened to describe a villain that was unnamed in the story but very obviously resembled a character in another person's story.
The fun for me is seeing who notices, but I can see where the owner might feel like being consulted first regardless.
Cameos = Goodness. Permission from character's owner = Doubly goodness. Using my character in your story during a cameo appearance = Allowable under one condition: Don't kill mah character off!
I don't have any stories up here -yet-, but I plan on writing one or two eventually. I'll let ya use two of my characters for cameos!
I'll think up a third character for ya to use to kill off.
*choke* heh, okay. I can't speak for anyone else here, but I'm not champing at the bit to kill someone else's character. Nice that you're flexible, though. 
Hey, no problem. -Someone- HAS to die usually, right? I can make a sacrificial lamb for ya to use.
I am, after all, an altaholic.
O_O Dude, in my opinion, it'd be AWESOME to see my characters appear somewhere in a story. Almost like an easter egg for those that know the characters around here. XD
I'm just waiting for you to post about some kind of robbery, with a certain pink android being kidnapped at the same time. XD
Actually I love this idea Cameos should occur more often in film and TV. Once permission has been gotten I say go for it!
Although it is hard for me to think these stories I've been readng would be improved any more than they are but have it
Looking forward to seeing them!
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The problem with cameos in film and TV is that there's too much money involved. Writers, producers and the companies they work for all hold claims to characters in their stories, and they hold onto them like their first-born. I think characters have to wait until they're on "public domain" before they're usable for cameos.
It's different for us, though. We've got no money coming back to us for our characters. As long as we feel our characters are being treated properly, we tend to grant permission easily. Heck, sometimes we even volunteer our characters for these moments.
My Stories
Look at that. A full-grown woman pulling off pigtails. Her crazy is off the charts.
When I was committing Legacy of a Space Ranger to electrons, I reached a point where I tried several different ways to setup a transition I needed to make. During the process of diddling with this and that, it amused me to imagine what a character from another story in this forum would think of the events I was writing about. When I settled on the transition I wanted to use, I wrote in an appearance of that character as a bit of fun.
I've got another story cooking, and I was considering writing in a cameo by a different character. It occurred to me that while I might like it as a kind of "in the know" gimmick, that the owners of those characters might not.
Note that I'm talking what you could call "background color" or an "easter egg", not a "guest shot". Writing ABOUT someone else's character is something that you ought to have their permission for, I'd think.
Hence, the general question - How would you feel about cameos? Like it? Hate it? Don't care?