Today I received N6VH's award certificate for the 2014 ARRL Ten Meter Contest.  The envelope had my name and address, but N6VH's callsign.  N6PN reported a similar thing happened to him. 
Obviously some screwed up the mail merge program.

In true ham spirit, I suggest attempting to contact the affected party by email, and if they want the certificate, just put some $1.20 in first class large envelope 2 oz postage on it, and mail it off.

The ARRL Contest Desk is well aware of the problem.

73,
Bob, N6TV