Just in from Marc Ambinder via the Nashville Post - as he says, doesn't mean that Bayh is the choice, but it is interesting:
NashvillePost.com has learned that senior campaign officials from the Barack Obama Presidential campaign are being dispatched from various locations around the country and are converging in Indianapolis for a "major event" to take place on Saturday.
Saturday is the same day that Obama is expected to make his first public appearance with his yet to be announced vice presidential running mate. Indiana is the home state of Democratic Senator Evan Bayh, widely considered to be on the short list of Democratic vice presidential contenders
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UPDATED:
Ambinder just posted that it is possible that advance teams are being sent to more than one city with other possibilities.
He also speculates the announcement will be tomorrow afternoon.