There are two types of people who visit Puno. People who go there to see the lake and then go right back where they came from, and people who go there on their way to Bolivia. As such, getting from Puno to La Paz is fairly simple and well traveled. It's also not completely safe and everyone is advised to do some homework and keeps their wits about. Think you're too smart a traveler to get into any trouble? Seen it all before? Hell I took a mini-bus in the Middle East and nothing happened to me! Well, tell that to people who were abducted on the road to La Paz. There was even a movie about it on Lifetime, we saw it 2 days after we got back!