From Jonathan Abrams at the Los Angeles Times:

...the Golden State Warriors have offered free-agent Elton Brand a more lucrative, multiyear deal than the Clippers have proposed, according to NBA sources who requested anonymity because they are not allowed to speak about other free-agent dealings. On Tuesday, the Clippers reached a verbal agreement to sign Warriors free-agent Baron Davis and were nearing a new deal with Brand.

Now, the Warriors have more salary cap space than the Clippers and have offered Brand a maximum contract, according to the sources.

Brand could not be reached for comment this morning.
The subtext of the Clippers' poaching of Davis has been that he and Elton have [unofficially] coordinated their decisions.  That's the hope, at least. 

UPDATE: From Chad Ford's live chat on ESPN.com: "I think [Elton Brand] opted out specifically so that the Clippers would have room to sign Baron. He'll be back in LA for sure ..."