Definitely make sure you that you transfer the Applecare over and ask the seller if he/she is willing to do so. It requires you to send in some information to Apple.
6. Transfer of Plan
You may transfer this Plan to a new owner of the Covered Equipment by sending or faxing
notice of transfer to Apple Customer Support, Hollyhill Industrial Estate, Hollyhill, Cork, Republic
of Ireland (fax number: +353-(0)21-428-3917). You must provide the Plan Agreement Number,
the serial numbers of the Covered Equipment being transferred, proof of purchase of the Plan,
and the name, address, telephone number and email address of the new owner.
-From AppleCare Terms and Conditions (Europe)