The official LOST podcast from LOST producers Damon Lindelof and Carlton Cuse says that in the 3rd season of LOST, there will be no re-runs! The first six episodes will run un-interrupted from November, ending with a mini-cliffhanger, and then will not air for the next 12 weeks. Upon returning in February, the show will air consecutive new episodes for 17 weeks until the end of the season.
They also say that during the 12 week break, no re-runs will be aired. This is, I think, good news, because at least there will only be one gap in the season, and we, as viewers, won't be tortured by stations showing old episodes.