Maine is one of two states that allocates some of its electoral votes by congressional district. (Nebraska is the other.)
Polls indicate that Romney will lose Maine as a whole, but the state’s second congressional district has a significant GOP presence. Whoever wins that district gets one electoral vote.
If liberal-leaning PPP says Obama is up by only 5 points, the district is possibly in play.
Pro-Romney ads have been running there:
You never know; it could matter.