I think a lot of it also depends on the school & the schools requirements for political education.
Here at UT, you only have to take 2 classes of government (6 hours total) for any degree outside of a Political Science degree. First class is how Government works, second is on a issue topic in Government that you pick (foreign policy, Congress, etc). Most of the teachers do a pretty good job at not injecting their opinions in those classes.
The upper-division classes are where you're most likely to find it happening. I've had teachers present a liberal or conservative slant, but they mainly use it for humerous purposes, nothing serious. Sort of a Jon Stewart approach to teaching I guess.
During actual discussion and teaching my experience has been extremely good. Teachers have just gave the facts here, and if theres an opinion based argument that is relevant, present both sides.
My class makeup (teachers are always curious about how their students think on the party ID scale) is usually about 40% conservative, 30% liberal, and 30% think of themselves as an independent/moderate.