According to several sources filming on the S.H.I.E.L.D. pilot is expected to begin mid January 2013.
The Walt Disney Company's Marvel Television division of Marvel Entertainment is currently in pre-production for a new television series pilot titled "S.H.I.E.L.D." for ABC. Casting directors in Los Angeles and New York are holding auditions for series regulars, recurring roles, and guest starring roles. The show's extras will be cast throughout the season, which begins shooting in Los Angeles mid-January, 2012. "S.H.I.E.L.D." will be set in the Marvel Cinematic Universe, sharing constancy with the films in that franchise.
(Note: 2012 above is clearly a typo)