Is he going bald?
In the new Mad Men Season 5 "trailer" they do a close up of Vincent in his Pete costume and makeup and his hairline is about two inches back from where it was last season.
http://www.imdb.com/list/RDuccS_NvmY/#play-all
See the preview thing up here ^^^
http://www.vimeo.com/jzcommunicate/albums