There's been a lot of noise on WebmasterWorld about a Panda 2.4 rolling update.

Google Panda 2.4 Underway? Nope. has confirmed with Google that there is no update taking place for the Panda algorithm currently.

Panda has been updated on a Monthly basis as follows:

Panda 2.3 on around July 22nd.
Panda 2.2 on June 18th or so.
Panda 2.1 on May 9th or so.
Panda 2.0 on April 11th or so.
Panda 1.0 on February 24th