According to Mike Francesa from WFAN 660, the Mets will announce the signing of Jason Bay "Early next week". This is, of course, pending the results of a physical, but it looks like Bay is headed to the prom with the girl he didn't want to go with, simply because he didn't want to stay home. Now maybe Red Sox fans will get over the "Jason Bay is returning" delusion. More info as we get it.
UPDATE: According to our good friend Ian Bethune at Sox and Dawgs, the Red Sox will receive a 2nd round sandwich pick from the Mets, as their first round pick (#7 overall) is protected. They also get a supplemental pick because Bay is a "Type A" free agent. Keep that in mind as trade rumors involving Red Sox prospects get bandied about, as they will be able to replenish the farm in June.
Audio of Francesa's announcement is right here- Bay to Mets