Well, since I was asked to chime in...
First of all, let me say that I think Les Misérables looks quite impressive. Certainly the trailer suggests that visually, Tom Hooper may have a lot more cinematic potential in him than The King's Speech suggested, and I like the fact that the cast is (mostly) full of genuine SINGERS. Plus, the widely-hyped singing-on-set aspect will likely be seen as a technical innovation that I assume will give the movie an extra boost critically and commercial. (Though, I have to say, both Tom Hooper and Anne Hathaway come off as totally pretentious in that ad that's been running in theaters -- they act as if every movie musical before this stunk because the vocals were recorded off the set.)
But until the movie's release, I have to say I'm not convinced it's the ace-in-the-hole Oscar-wise that some do. As Mister Tee said, Dreamgirls was widely seen as the odds-on favorite to win at this point (including, admittedly, by me), and Nine -- with all those Oscar winners involved -- was seen as a major player until the reviews hit. And talk of Sweeney Todd as a possible winner was widespread as well, during a period when a lot of people thought No Country for Old Men was far too obtuse to actually prevail. It's possible that major Tony victories for all of these musicals gave people the assumption that these properties would automatically garner awards in another medium.
But my biggest hesitation about declaring Les Mis a probable Oscar sweeper has to do with statistics. As we know, Best Picture and Director typically go hand in hand, and films that are strong Best Picture candidates almost NEVER lose Best Director...but do people realize how hard it is for a director to win Picture and Director two times at bat?
Unless I'm in error, I only count TWO living directors who have accomplished this. Screen legend Clint Eastwood, in a twelve year period, and with a likely second-place finish in both categories in between. And Milos Forman, in a nine year period.
A number of directors have come close, only to come up one trophy short -- Spielberg in a five-year span, Oliver Stone over three years, and Coppola in two. Note the status of director we're talking about, as well as the fact that the losses in every case were considered significant upsets.
Going further back, we see these double-double wins with a bit more frequency -- Kazan, Wise, Wilder, Zinnemann, Lean, Capra, even triples for Wyler -- but in all of those cases, the directors had additional nominations prior to their wins, or losses in between. And in many cases, significant time passed between the sets of wins. Which is, to say, directors usually have to have a fairly healthy Oscar resume in order to win that second Picture/Director pair, and it usually won't come right away.
And, even in the studio era, we still saw big-deal directors come up a prize short; Ford and Mankiewicz nearly accomplished back-to-back doubles, but missed a Best Picture prize.
You can probably see where I'm going with this. Tom Hooper is still considered a young director. He's only on his third feature. His last film -- only two years ago -- won Picture and Director. Many grumbled about his victory in the latter category. Statistics seem to suggest he'll have quite an uphill battle to a repeat so soon.
Which, of course, isn't to say it couldn't happen. But I think it's worth a lot more consideration than some people have given.
EDIT: Oh, and I'm sure some folks will argue that Les Mis can be a strong frontrunner even if voters have decided Hooper has had enough reward in the Best Director category. But some of us know better than to bet on a split like that, especially this early in the game.