But by splitting it in two they won't have to radically truncate a great deal of scenes and they can leave in moments like [spoiler]the wedding, Dobby's final moment & burial, freeing the dragon (er, doesn't that sound naughty!) and the visit to Luna's house[/spoiler]. It's also important to give the epilogue it's proper amount of time and not rush it (kinda like LotR had a long triple ending).

HBP had some scenes that could be left out like dwelling on the effects to muggle-world but DH has so much that's important on the quest.

The guessing game would be where they will split it. I'd have to go re-read a couple parts to remember where the middle actually is - was it after [spoiler]he buried Dobby[/spoiler]? Because I liked his attitude much better after that...