When Lucky Star began airing, the show's director was Yamamoto Yutaka ("Yamakan", as he is often referred to). However, after 4 episodes, he was taken off the project and replaced by Takemoto Yasuhiro (one of Kyoto Animation's longer-time directors), who went on to direct the remainder of the show.
What happened? This is the only time in KyoAni's history (since they started being a main production studio in 2003, anyway) that a show's director has been changed midway. Kind of weird, huh?
I'm aware of the general belief - that Yamakan's direction of the first four episodes was so bad that they had no choice but to get rid of him - but I'm looking for specifics, preferably from the mouths of the people involved.