Speculations are abound on one of JG's fansites. Jakey is wearing a heavy beard and moustache (Gawd, I do hate the hair on his face.) He seems awful sad and lonely. According to the snapshots of him on the net he's showing up wearing the same pair of jeans, sometimes the same ratty black shoes and lately the same t-shirt. You know the one with the stamp on it.
Personally, I think the reason why Jake is appearing worn around the edges is due to this new character he's playing in Zodiac. Staying in character and keeping it on the edge.