Insider content on ESPN.com, I'll just cut/paste the relevant part re: Matt Cain:
"2. As the Giants consider ways to bolster the power in their lineup, GM Brian Sabean can go into the winter knowing that he can probably add a major hammer, if he ever decides to dangle Matt Cain, and two options could be Ryan Howard and Prince Fielder. Each of those sluggers has failed to reach long-term deals with their respective teams, each will see their salary escalate quickly through arbitration, and the Phillies and Brewers would love to add a power arm like Cain. "The Phillies could go out and find somebody to drive in runs in their park in place of Howard," said an AL general manager. "But in that bandbox, they will always have trouble finding pitching. Cain misses bats; he'd be perfect for them." And after this season, the Brewers will lose CC Sabathia and Ben Sheets to free agency, at a time when they have emerging position prospects; they can find somebody to play first but will need an anchor for their rotation, and Cain would serve that purpose."
While I would absolutely hate to lose Matt Cain because he is just an absolute stud, I think that any rational GM would have to consider doing a Cain-Howard or Cain-Fielder deal, especially given the strength of our starting pitching down in the minors.