Just watched the 3rd season premiere. It looks like at least for the first half of this season, odd-numbered episodes will take place in the alternate dimension, while even-numbered episodes are set in our reality.
Notable guest stars for Season 3 will include Amy Madigan (Carnival), Andre Royo (The Wire), Kevin Weisman (Alias), Shawn Ashmore (X-Men) and twin brother Aaron Ashmore (Smallville).