Some great advice in the thread so far.
Another angle you can use, to get some backgrounds being built is basically bribing your players
"All those who build me a background for their character will be rewarded with a magic item."
I did this with my players but with a slight twist. I had them tell me what they wanted their magic item to do. The condition for the introduction of this custom made item into the game was that they had to tie the object into their back story. I also worked with them on this to make sure the balance wasn't skewed too much (not that I worry about balance as I make up for it by hitting them extra hard). This item will increase in power, moving towards the 'full' version of what they want it to be able to do as they reach key levels and complete Backstory related adventures.
Dangling a carrot will give them a mechanical reason to start thinking about who their characters are, which is not a bad place to start.
This provided me with loads of adventure hooks which I have been able to spin in and out of the main adventure line.
Another carrot you can tangle are Drama Tokens. In a nutshell this is a houseruled reward system I have implemented into my game. I use Drama tokens to get my players acting swiftly on their turn. Basically they represent a +1 bonus to any dice roll that can be added at anytime. I let them stack to a max. of +3. I don't allow these tokens to carry over sessions, but I allow the players use unused tokens to buy Drama Cards (not entirely dissimilar from the cards WotC has just brought out whatever they are called)

Anyway ... they are small, neat mechanical rewards that they can pull out every now and again and turn failure into success. You could invent yourself a similar reward system for good Roleplaying.

If you decide to do something like this, you will need to explain to your players explicitly how this works, why you are doing it and get feedback about how they feel about it.
As for how to encourage roleplaying during actuall play, I'm pretty strict with my players. I never allow my players to get away with" 'I bluff the guard'. Picks up dice to roll Bluff* "
My response might be something along the line of:
'I will decide whether you are bluffing the guard or not once you tell me what it is you say to the guard. Depending on what you say I will also decide whether any dice need to be rolled or not. PUT THE DICE DOWN!'
I have also introduced a system that discourages Metagaming. When it gets out of hand I simply take one of my blood red 'Karma' Tokens and put it on the table. I can use these for any of my monsters during the session as an Action Point. Metagaming causes bad karma for my players quite literally.
I think it's important for players to distinguish between what they know and what their character knows. My players can be very lax about this and often tactical discussions about what to do out-of-character just go on and on and on and on and on and ... you get the picture. During the middle of combat ... really? You're talking about this????
If players are going to metagame, they should at least be inventive and creative about disguising it in-character. "Lads, let's take a breather, that Orc chieftain bruised my ribs and my arm is tingling a bit" vs " Let's take a Short Rest, I need to recharge my encounter powers before we get into the next fight" or "I need to pray a bit" vs "I've used both of my Healing Words, need a Short Break"
I also quite often take players out of the room to relay important information they individually have aquired, say via a knowledge check for example, forcing them to communicate it to the group in character. I stress that if the character hasn't relayed the information, the others are not allowed to act as if they knew it, even if their player does.