Go ahead, think of a character and watch him guess it. (http://us.akinator.com/#)

This sort of thing is sort of old news around the internet, I suppose, but hey.

So far it's successfully guessed:
Funky Kong
Rydia (Final Fantasy IV)
Miles Edgeworth (in 17 questions)
Mikau (Zelda: Majora's Mask)
Falco (16 questions)
Wendy Oldbag (Ace Attorney series) (17 questions)
Adrian Andrews (Ace Attorney) (19 questions)
Balrog (Cave Story)
Dave Strider (18 questions)

Took more than 20 questions to get Sergei Dragunov (Tekken), and Katie (Horton Hears a Who). I had to introduce him to Max (Pangya) and Earl Devereaux (Cloudy with a Chance of Meatballs).

Fun for some reason!

e: Just got Kit Fisto.

It failed on Jon Arbuckle and Professor Moriarty.

Got Tabuu, failed on Bill (Star Fox 64), after guessing Peppy, Fox and then James McCloud.

...Speaking of James McCloud, let's see if he can get the F-Zero character.

...After 30 questions, yes.

Edit: Was quick to guess Rosalina of Super Mario Galaxy and even Landfill from Beerfest. Then guessed the Rathalos (Monster Hunter) in 19. Hoopy!

e: Tried to get it to guess Fatalis (Monster Hunter). It guessed White Fatalis, which was dumb of it because it asked me twice if it was white and I said not usually. I went with Not Exactly, which it interpreted as No, and proceeded to guess two more incorrect monsters. Ho!

It failed to guess "Spadge", the uncle of Boggy B.
It did however guess "Worms" as a generic character after about 16 guesses, but I couldn't accept that.

Later, when added my character, it suggested that I might thought of Martyn "Spadge" Brown. :D

Holy hell it knew Storm 1.

It got Kurt Hectic (protagonist of MDK).
It failed to get Kurt's dog however (Max)

It knew The One Electronic, Samurai Jack and Manny from Black Books.

i was curious how long it would take to get barack obama. took 12 questions

Found Gordon Brown fairly quickly.
Found Tony Blair after a while.
Found John Major (quicker than Blair).
Found Margaret Thatcher after ages (if it had used the same set of questions it used for Brown it would have found her very quickly).

And Alistair Darling (current Chancellor of the Exchequer); very quickly too.

Gadzooks, it got the Wizard of Yendor on the first guess.

Beat him pretty good with Jinpachi Mishima, though, end boss of Tekken 5/Dark Resurrection. He did guess Heihachi at 25 questions, which was an excellent guess but not quite. I think he actually went to 40 questions without getting it. Turns out I was only the 4th person to play Jinpachi.

He then guessed Abe Sapien from Hellboy with alarming efficiency.

He's very good with video game characters, probably because that's who everyone plays.

Just tricked him with Robert Goddard! (father of modern rocketry)

Later, when added my character, it suggested that I might thought of Martyn "Spadge" Brown. :D
Oh hey I added him as an answer over a year ago. Good to see it's still on the database.

So far it's successfully guessed Skull the Troll (from PvP) and Serious Sam.

nice, it got fawful in 25