After seeing this article over at Think Progress I took a quick look at the data on Obama's approval rating throughout this year.
Note the trendline of Rasmussen stays a good 5 points below that of all other polls. The two never cross, nor do they even come close.
Statistically speaking, error in polls can never be eliminated, but it should not always err in the same direction. Somebody has a flawed polling model, either Rasmussen, or everybody else.
"Everyone is entitled to their own opinion, but not their own facts."
- Senator Daniel Patrick Moynihan