As of last this past weekend, Innistrad is now legal in all constructed formats. At that same time the normal yearly rotation for standard and extended also took place.
Cards from the following sets are now legal in Standard:
Scars of Mirodin
All of Zendikar Block (Zendikar, Worldwake, and Rise of the Eldrazi) as well as Magic 2011 rotated out of standard.
The following sets are in the currently in extended:
Shards of Alara
Rise of the Eldrazi
Scars of Mirrodin
As always, any version of a card is legal as long as a version of a card appears in a legal set. For example, a copy of Ancient Grudge from Time Spiral can be played in standard and extended as that card has been reprinted in Innistrad.