They wanted a "slow burner" but so far its selling like mad, so IMO its no flop FAR FAR from it.
Sure, it should have legs.
And i don't want to call it a flop, especially from the gamers point of view.
But Sony neither wanted it to sell as slow as possible, nor just to the existing user base.
IMHO, looking at Wii BF sales, it doesn't stopp people from buying wiis. We will see if move is the new HW-seller for PS3, but it looks like the slim version had much stronger impact than move, so far.