I'm far, very far, from being an expert on the US football team, but they strike me as a team who is solid and hard working enough to do well against a favorite that has the possession, but not as good against teams of their level.
At the world cup i expect them to suffer much more when they'll play "Ghana" or "Serbia" than when they'll play against the group's favorite.
Of course, much depends on the type of football their opponents will play. Every single team has a dark horse which doesn't suit them at all. The US team isn't a strong favorite that can adjust to different styles and steal a good result even when playing very bad, so lots will depend on the style of the teams they'll get in their group.
The USA are a team that can top the group and yet, they're a team that can easily end 4th in the WC group.