The September 1, 2008 Banned and Restricted List announcement is up. Here are the changes:
Extended
Sensei's Divining Top is banned
Legacy
Time Vault is banned
Vintage
Time Vault is restricted
Chrome Mox, Dream Halls, Mox Diamond, Personal Tutor, and Time Spiral are no longer restricted
I don't have much of an opinion about the eternal formats, but there's already some discussion and dismay about the banning of Top in Extended. The explanation will come later on this week in the upcoming Latest Developments column, but if I had to guess, I'd think it would be a time issue. Decks that run Top benefit from using it every turn, and each activation adds time -- sometimes, a lot of time -- to each turn. Over the course of a match, and then over the course of an entire tournament, that's a ton of extra time. Extra time means more matches going to time, more draws, and a general train wreck for most tournaments.
That's my guess, at any rate -- not power level issues, but time.