The Rays began the day with 36 players on the 40-man roster. Today they purchased the contracts of RHSP Wade Davis and RHRP Dale Thayer from Triple-A Durham and purchased the contract of LHP Jacob McGee from Double-A Montgomery. Since no one was removed from the 40-man the total stands at 39. This is important for several reasons, if the Rays sign a free agent or trade for a player between now and the December 11th Rule 5 draft they can add him to the roster without having to drop someone else and risk losing them in the draft. This also allows the Rays to participate in the Rule 5 draft because you can't draft anyone if you do not have an opening on your roster.
Davis and McGee were no-brainers and Thayer was quite good at Durham this year. As a relief pitcher, Thayer was likely to be taken as relief pitchers and outfielders are often taken in the draft because they are the easiest to "hide" on an active roster if they aren't quite ready for MLB. Anyone selected in the Rule 5 draft must be kept on the selecting team's 25-man major league roster for the entire season following the draft. An outfielder can be a 4th or 5th outfielder who is used as a defensive substitution, a pinch hitter or runner, but basically doesn't see much action. A reliever also can fill a role without being used much, such as in mop-up situations where the game is already out of hand.
You may wonder why adding McGee was necessary since he just underwent Tommy John surgery and is unlikely to see any action until late in the season, making him useless to a selecting team. The rules state that an injured player can be placed on the disabled list, opening another spot on the selecting team's 25-man roster. Another team could have selected McGee, put him on the DL and let him rehab until he was health enough to activate, and come away with a highly rated prospect without hurting their active roster. There are some limitations to using the DL, McGee would have to be on the selecting team's active roster for 90 days or else the requirement that he remain on the 25-man roster would extend into 2010. For example, if he were activated for 30 days in 2009, he would have to remain active on the major league roster for at least 60 days in 2010 to satisfy the Rule 5 requirements. None of this really matters now that McGee is on the 40-man roster, but I wanted you to know why he was definitely a risk of being taken despite the injury.
I'm working on an article detailing the Rule 5 draft and will make sure to post it prior to December 11th. It's turned out to be a large project (and article) so don't expect to see it for a week or two. If you have any specific questions about the draft post them in the comments or email me.