Well, it was fun while it lasted. According to the folks at Dream of Italy and Tony Polzer from 3 Milennia Tours, the Roman Forum will begin to charge admission as of March 9th. Tony lays out the facts, including admission and access, on the Slow Travel forum.
We have not been able to independently confirm this development from a press release. But we hope to find info about this on the Comune di Roma or Romaturismo sites soon. In the meantime, you can read our post Saving Money with Combined Tickets, which has details about the Roma Archeologia card.