There are a few small areas of East Falls, like the area near Germantown or the area near North Philly, that are not entirely safe. And in parts of East Falls they really don't like outsiders. When I was in college I lived there and got my tires slashed, car keyed, etc. But it is not an "unsafe" area in the traditional sense of the word. And there are some absolutely beautiful areas of the neighborhood. The governor of Pennsylvania lives there, as well as one of our senators.
Roxborough and Manayunk are pretty much safe all around. Your biggest concern in Manayunk is drunken college kids. I just bought a house in Manayunk and so far it's been very peaceful.