This was already being discussed in this FanShot but I thought I'd make a front-page post with some more information, as well as a few thoughts.
Here's a good summary from my colleagues at Baseball Nation, including the three possible scenarios that could result:
(1) The Red Sox deny the Cubs' request
(2) Epstein denies the Cubs' request
(3) The Red Sox grant the Cubs' request under the condition that they are compensated if Epstein is hired away
On the surface, hiring Epstein looks like a good idea. He will cost a lot of money, and if you are concerned about a GM who hands out long-term deals to players who then don't produce, Epstein has had quite a number of those in recent years: Daisuke Matsuzaka, John Lackey, Carl Crawford, among others. The problem of possible compensation is also an issue; presumably the Red Sox would ask for quite a bit, since Epstein is under contract for another year.
This is far from the end of this story; it may not even be a beginning if Boston says no. But yes, this is worth discussing. Have at it.