Really, the key is the health of the players. Halladay, Lee, Oswalt and Hamels are not likely to make every start and then key players have nagging injuries throughout the season. Losing 4 in a row isn't very many if the team is hurting or goes through a bit of a slump. It's a long season and anything can happen.
I'm expecting the Giants to cruise through the NL West and easily pass 100 wins, as they only had 92 last year I believe, but that being said, it depends on the health and affectiveness of the team as a whole. Looking for a Giants/Phillies showdown once again for the pennant.