Some speculation from Sean Deveney at the Sporting News:
The motivation for his decision to opt out was that he could put pressure on the Clippers to improve the roster, to make the team better by spending a little money. They did just that. So Brand should have fallen in and re-joined the Clippers. But five days have passed and Brand still hasn't signed.

It's worth asking: Why not?

"It makes sense for Elton to wait till the salary-cap numbers come out, because then he knows exactly what teams can offer and what his options are," says one league source. "He wants the max. He can put the Clippers in a situation that they have to give it to him."

One general manager agreed. "I don't think Elton really wants to leave the Clippers, but he wants them to pay him, too," he said...

If L.A. wants to keep Brand, the only way to ensure it happens is to up the offer. Otherwise, by the end of this week, we could have our second shocker of the free-agent period.

There's some irony here. By opting out, Brand clearly put pressure on the Clippers to spend more money on other free agents. What isn't clear is whether he can put enough pressure to get the Clippers to spend more money on himself.

My most cynical sense is that Brand's initial posture -- "Show me you're serious about winning, and I'll stay" -- was based on his belief that the Clippers would never be able to attract the talent to demonstrate their seriousness, which, in turn, would give him cover to walk.  But when the Clips landed Baron Davis, it left Brand in the awkward position of having to either live by his word -- and forfeit $20M -- or leave and break his tacit commitment. 

Again, this is the least generous read on the situation.  The more hopeful one is...hopefully...more likely.  And the best case scenario is here.

UPDATE: Marc Stein gets into the numbers:

...Even if Brand is not interested in the extra sixth year that only the Clippers are allowed to offer him and insists on a five-year deal -- as my tireless colleague Tim Kawakami of the San Jose Mercury News reports -- L.A. can still assemble a five-year deal worth $80-85 million and give Davis his estimated $65 million over five years.

Upping their reported five-year, $70 million offer to Brand depends on how many of the following free agents that the Clippers are willing to renounce in addition to possibly waiving Josh Powell: Corey Maggette, Shaun Livingston, Quinton Ross, Nick Fazekas, Marcus Williams, Paul Davis, Dan Dickau, Boniface N'Dong, James Singleton and the immortal Smush Parker.

So...

We might eventually be looking at a difference of only $10 million or so between the two contracts, as opposed to the widespread assumption that the Warriors are offering some $20 million more than their Pacific Division co-tenants ... as long as Clippers owner Donald Sterling is willing to go to the five-year max.

No matter how jittery Clippers officials might be about Golden State's rich offer -- as we also keep hearing -- Sterling shouldn't have much to fret about if he's willing to nudge Brand's new deal past the $80 million plateau. I struggle to see a shortfall of $10 million or $12 million or anything in that ballpark convincing Brand to walk away from L.A. to join a Golden State team that suddenly has a major hole at point guard as well as a younger core than the team he'd be leaving.

It's especially hard to picture that scenario when you factor in Brand's well-chronicled love of Hollywood, his one-of-a-kind pride in being a Clipper and the fact that Brand, as ESPN.com reported last week, specifically told Clippers management during negotiations on a contract extension in June that Davis was the player he hoped they'd pursue if Davis became available in free agency.

 Why Elton might not be interested in year 6.