The San Francisco 49ers opened as fairly significant favorites over the Baltimore Ravens when the 2013 Super Bowl odds dropped, but the line is already moving towards the AFC Champions. When the opening line came out, the Niners were five-point favorites, but they've already dropped to four-point favorites at every book tracked by OddShark.
Odds are interesting to me, simply because it's interesting to speculate about what Vegas is going for. Generally, the idea is to generate an equal amount of betting on each side to ensure a profit for books, but that hasn't been the case early on in wagering. If the spread has already dropped by a full point on the Tuesday following the conference championship games, there's a lot of money going on the Ravens.
I'm assuming that the line was set where it was because the Niners have a massive fanbase, while the Ravens have a passionate, but much smaller fanbase. Unfortunately for Vegas, most of the people who gamble at least attempt to bet with their brains, not their hearts, and +5 is a nice number for an even matchup. I don't think that line will move back up until it gets under +3.