Not at all, really. The similarity is the playing of cards to advance toward a goal, and playing of "stop" cards on other players to stop them advancing.
The biggest difference is the reason for playing stop-cards: in Mille Bornes, you just want to be ahead of everyone else. In Saboteur, you're on a team with other players trying to reach a goal, and you're mainly trying to figure out who's on the other team to stop them from interfering with your team's plans.
The gameplay possibilities are also much wider in Saboteur. There is a spatial element in the playing of the path cards, which is completely missing in Mille Bornes. The different roles also have varied ways of winning. Getting closer to your goal, without making it obvious to other players or teams is much more interesting than just playing the greatest mileage card repeatedly.
The biggest difference is the reason for playing stop-cards: in Mille Bornes, you just want to be ahead of everyone else. In Saboteur, you're on a team with other players trying to reach a goal, and you're mainly trying to figure out who's on the other team to stop them from interfering with your team's plans.
The gameplay possibilities are also much wider in Saboteur. There is a spatial element in the playing of the path cards, which is completely missing in Mille Bornes. The different roles also have varied ways of winning. Getting closer to your goal, without making it obvious to other players or teams is much more interesting than just playing the greatest mileage card repeatedly.