I dunno... if you watch the teaser trailer, it sounds like Heath's got things pretty well-in-hand.... he's got juuuust enough of Nicholson's Joker in there, but a lot of his own thing, too. Harder-edged. And Michael Caine has been put down as saying that Ledger is giving an astounding performance. I know that he's probably pretty well-inclined to praise the film, as he also happens to still be in the middle of shooting it, but still... someone with as much class and experience as Caine probably wouldn't toss words like that around unless he meant them.
Word on the street is that Ledger's Joker is going to have scars where his cheeks were cut open from the corners of his mouth to nearly the jawbone. I can't remember what that particular bit of torture is called, but we knew it as a Frisco Smiley where I grew up. I've seen pictures to corroborate, but the only ones left look doctored... Warner Brothers seems to be keeping on top of PR leaks pretty well, and what they don't want seen gets taken down the minute it's up.