It's early days, yet, but a quick tour around the top tables of the Grand Prix and the sixty or so decks on display gave some interesting insight into what's popular and what's winning.
The format's four pillars are all strongly represented, but not overwhelmingly so. Of the Rock family of decks (those built around the skeleton of hand disruption and cheap green threats) it seems that straight black-green is outpacing the versions that touch white for Lingering Souls. The better mana allows them a few more man-lands and a little less pain. It's the same story among Splinter Twin decks, with players relying on the strength and consistency of a two-color build rather than splashing for Tarmogoyf. Affinity and Pod boast fewer players than the other two, but are still numerous. Burn decks continue to lobby to be included as a fifth pillar, also putting up strong numbers.
The big surprise so far is the number of players putting faith in blue-white-red. These decks fall into a spectrum ranging from pure control styled after Shahar Shenhar's World Champion list, through the midrange Flash versions that add Restoration Angel and Blade Splicer, and ending on the beatdown versions that hit hard with turn-three Geist of Saint Traft. Grouped together they are easily the most numerous deck.
The other breakout seems to be Scapeshift. The format's "other" combo deck, it gets an edge from not having to worry about protecting nonland permanents, only surviving long enough to resolve a single spell. If players have put away their Leylines of Sanctity and Blood Moons, then the Scapeshift player can run wild.
And of course it seems like there's one of everything out there. I saw Mono-Blue Tron, Infect (which I thought would be more popular after its results in GP Boston-Worcester), Living End, Delver, Bogles, and even a dedicated Mill deck complete with Hedron Crabs and Archive Traps. I'm definitely rooting for that guy.