If the King’s Speech wins, it will become the first film in 83 years of Oscar history with a British monarch as the central figure to win Best Picture. [source]
If the Social Network wins Screenplay, Editing, Directing but then loses Best Picture it will join the ranks of only two movies in Oscar history to do so:
A Place in the Sun
Traffic
In the years that Oscar has split with Picture/Director, only twice has the DGA winner lost the Oscar for Best Director but then had the film win Best Picture:
Crash (Did not win DGA)
Chicago (won DGA, The Pianist won BD)
Gladiator (did not win DGA, Traffic won BD)
Shakespeare in Love (did not win DGA, Saving Private Ryan won BD)
Chariots of Fire (did not win DGA, Reds won BD)
The Godfather (won DGA, Cabaret won BD)
In the Heat of the Night (did not win DGA, The Graduate won BD)
Around the World in 80 Days (did not win DGA, Giant won BD)
An American in Paris (did not win DGA, A Place in the Sun won BD)
If the Social Network and David Fincher win on Sunday, they will be the third to win without the DGA:
Ron Howard, Apollo 13 (PGA, DGA, SAG, SEFCA), lost to Mel Gibson, Braveheart (Globe for Dir, BFCA for Best Dir, Eddie, WGA)
Steven Spielberg, the Color Purple (NBR, DGA) lost to Sidney Pollock, Out of Africa (won Globe)
Anthony Harvey, the Lion in Winter (won Globe, NYFCC, WGA, DGA) lost to Carol Reed and Oliver (won Globe)
The chances are better for The King’s Speech to win both Picture/Director, or The Social Network to win Picture or Director than for them to split. But, as Scott Feinberg pointed out, if you do predict a split you have a better chance of getting one or the other correct.
If Tom Hooper wins the Oscar for directing, he will one of four directors since 1975 to win it with only the support of the DGA, without winning any other major group. ¬†The other three to do it were Rocky (which won the LAFCA),¬†Rain Man and The English Patient, but all three won the Globe for drama and the Eddie. ¬†The King’s Speech has won neither.
Prior to 1975, more directors won the Oscar for directing with only the DGA behind them (only two films had what TKS currently has):
And they were:
1952 – John Ford, the Quiet Man, won NBR for Best Picture, lost to Greatest Show on Earth for Pic
1955-Marty, won NBR+NYFCC for Best Film, won BP/BD
1961-West Side Story, won Globe, NYFCC, won BP/BD
1969-Midnight Cowboy, won BP/BD
1970-Patton,  won Eddie, Globe, MPSE, NBR, won BP/BD
1973-The Sting, won Eddie, NBR, won BP/BD
1974-The Godfather Part II, won BP/BD
And then, ground we already covered: The Social Network, should it lose, will be the first film since the Globes began to win the NBR, the NYFCC, the Globe and then lose the Oscar.
In the years when Oscar had ten Best Picture nominees and a preferential ballot, there was a Picture/Director split:
Rebecca (won only 2 Oscars) / John Ford for The Grapes of Wrath (also won only 2 Oscars)
The Life of Emile Zola (won 3 Oscars) / Leo McCary for The Awful Truth (won 1 Oscar)
The Great Ziegfeld (won 3 Oscars) / Frank Capra for Mr. Deeds Goes to Town (1 Oscar)
Mutiny on the Bounty (won 1 Oscar) / John Ford for  The Informer (won 4 Oscars)
[alert]please let me know if I’ve gotten anything wrong[/alert]