[mhagain]

My predictions:

We're going to have some kind of flashback/prologue thing; not sure what it could be (maybe Dain seing Durin's Bane through the doors of Moria after the Battle of Azanulbizar, maybe Bilbo and Frodo talking about something in Rivendell during the LotR timescale, maybe something else), but that's the start.

The destruction of Lake Town and death of Smaug: this is a single incident in the book, but I suspect that Jackson is not going to be able to resist splitting it into two separate incidents for the movie. Depending on how badly he wants to wreck the storyline, he may even leave Smaug alive until after the Battle of Five Armies - I actually feel that this is most likely. My prediction is that Smaug will destroy Lake Town then fly away somewhere; some time later Bard will sneak back in, the Dwarf Ballista will still be intact, he may even disassemble it and move it somewhere else, then kill Smaug. After the Battle of Five Armies - you heard it here first.

This approach will give Jackson 3 big action sequences at Erebor - the destruction of Lake Town, the Battle of Five Armies and the Death of Smaug; plenty of room for padding there.

The Necromancer storyline will need to be resolved. Gandalf is currently captured so he'll either escape or be rescued. My bet is that Radagast is going to rescue him, or at least be involved in the rescue/escape (Gandalf's attempt to send him off to Rivendell for help in DoS obviously having fallen on deaf ears). There will be another moth/eagle thing during this scene too.

From there we'll have the White Council meeting, Saruman is going to stall, perhaps we'll see the beginnings of his treachery (I think this likely too), somehow they'll agree to assault Dol Guldur and drive out the Necromancer.

That's also going to be another big action sequence, and I don't think Jackson is going to be able to resist intercutting it with the Battle of Five Armies. Of course that's going to completely mess up the story from the book as we won't have Gandalf at the Battle, but when did that stop Jackson before?

We need the build-up to the Battle of Five Armies, including the initial stand-off, the Orcs coming, then followed by the Battle itself. Something to do with Thranduil not wanting to fight the Orcs but Legolas and Tauriel persuading him will probably happen; this has echoes of Theoden's initial reluctance to help Gondor in Jackson's LotR and I consider it likely.

There will also need to be lots of Dwarf action with Dain coming on the scene (I suspect he'll arrive earlier than in the book).

The Nazgul: these are almost 100% likely to make an appearance at some stage, but I'm not sure where or how. At a rough guess we'll see them taking Minas Ithil and turning it into Minas Morgul.

The death of Thorin: if as I suspect Smaug is going to be left alive until after the Battle, it seems likely that's how Thorin will die: Smaug will kill him. Otherwise he'll die during the resolution of the Azog/Bolg thing. Expect a fairly drawn-out scene.

The Arkenstone: Bilbo will probably steal it and hand it over just as in the book. This may be complicated if Jackson intercuts the Battle with the assault on Dol Guldur as Gandalf won't be there, but it needn't be impossible to resolve.

Azog/Bolg: Bilbo's going to kill one of these. Guaranteed. That's how he's going to get respect back after the Arkenstone. Otherwise no idea how they'll play out.

The Return of Gandalf: after the battle, and with a "well Bilbo my lad, you managed quite well there". There's really nothing for Gandalf to do during the Battle, even in the book, so I consider this likely.

Crowning of Dain as King under the Mountain: something similar to Aragorn's crowning in RotK perhaps? Another drawn-out scene. Hopefully the involvement of Billy Connolly isn't going to see too many slapstick elements enter, but I fear it will.

Establishment of Balin's Moria colony: a LotR link that we'll probably at least have mention of.

The Ring: I haven't even touched on this at all, but there's going to be lots of build-up to LotR here. I also think Gollum is likely to return.

The Journey Home: we don't have a RotK-like ending in store here, but Jackson's almost certainly going to find a way to drag it out. We may see a young Aragorn in Rivendell. Possibly no auction. Sauron will re-enter Mordor and the whole thing will finish on a very foreboding note; something like "your adventure is over Bilbo, but I fear that the real story has yet to begin..." - roll credits.

That's my best guess of how things are going to work out for the third movie, and it's easy enough to see where Jackson's got plenty of scope to make a 3-hour job out of it all.