There is not a great source on the Internet for info about tonight’s arbitration deadline.  I’ve found a lot of outdated links so far.  Maybe collaboratively we can create a guide to it in layman’s terms here.  Below is my understanding of the rules and tonight’s deadline.

Tonight at midnight EST is the deadline for teams to offer arbitration to their former players who have filed for free agency.  If arbitration is not offered, the team can still negotiate with the player but cannot receive draft pick compensation if he signs elsewhere.  Only Type A and B free agents result in compensation, anyway.

If his old team does not offer arbitration, the player can still sign with that team and be eligible to play on Opening Day.

This is all separate from the non-tender deadline, which is December 12th.  That is for players under team control (less than six years of service time) who do not have contracts for the 2008 season.