Avery Johnson was fired by the Mavs today; he's got a .735 winning percentage, and took his team to the Finals two seasons ago. However, the Mavs have lost 12 of the last 15 games in the playoffs under Johnson. He and Cuban didn't get along, and I guess Cuban thought the team needed a change.
There are also rumors that Mike D'Antoni could be on his way out in Phoenix, due in part to issues with Steve Kerr. This could be another one of those "change of scenery" type of moves.
Lastly, there's the Charlotte hiring of Larry Brown. I think it's an interesting fit; that team has some great young players, and a lot of potential defensive talent (Okafor, Wallace). It'll be interesting to see if Brown gets them all to mesh.