I tend to get word diarrhea when it comes time to put down a character's backstory.  I restrict myself to less than a page, though.  More than that, and things just get masturbatory.

And a lot of does depend on system.  WFRP is kingly in the way it forces the player to think on his feet about his character's life.  Why is a Marienburger Ratcatcher with cystic acne trying to get to Araby, anyway?

Then you have games like Exalted, where half of chargen is spooging out an epic poem about your travails and exploits before you ever roll a single die in anger.

I had a character once with a very long and detailed history who had a delusion that he was "just a character in somebody's RPG game" (yes, it was a modern-day game).  

Every time something bad would happen, I'd say in character "Blasted player!  Roll some different dice!"  At which point, I'd pick different dice to roll.  The schtick was funny for about half the game session and then I left it alone.

EDIT: But, he did have a very long and detailed history, something on the order of 2500 words or so (about 2 1/2 pages, typed).

I like something between 50 words and a page.  But it depends on the situation  For a one shot, 5-10 words of personality description might be enough. I hate super long descriptions that don't match the character sheet, like a long heroic history from a 1st level character.  I also hate the munchkin approach of justifying extra powers because it's in their background - nope, you should have built your character that way;  I'm talking about big things like ability to fly, use magic, talk to god, or such based solely on a line in the background.

As a DM, personality, outlook, and goals are more useful than history usually.  I don't care what your grampy's name was or what he did, knowing that you are searching for his lost ear is enough.

Quote from: NicephorusAs a DM, personality, outlook, and goals are more useful than history usually.  I don't care what your grampy's name was or what he did, knowing that you are searching for his lost ear is enough.

Good point.  I think a 3x5 card summary of a longer background would be most useful from a GM standpoint.  Trim away the fluff and dungeon dressing and you've got fifteen square inches of plot hooks.

I mostly GM and my view is you can have as long a background as you wish as long as you don't expect me to read the bloody thing.

Seriously, if you can't sketch an interesting character in a paragraph or less you're not trying.  Don't write down the good stuff, show it to me in play for god's sake.  I game to game, not to read.

Harald is a young man recently come to Iceland after being outlawed in Denmark, where he was involved in a kinslaying.  He is a large man, powerfully built but with a wary air.

See that above?  That for me is entirely adequate.  Does he still have family back home?  Was he guilty of the kinslaying?  Is he being hunted?  Don't tell me, let's find out in play.