It's about as safe as anywhere in Mexico. Baja Sur is indeed one of the safest states with a murder rate of just 35 per year according to the economist. Chihuahua and Guerrero are the most dangerous places. Acapulco is the state capital of Guerrero and has become quite bad in recent years, despite it's former reputation as a glitzy tourist hot spot.
As bad as Mexico is though, it's not as bad as some other Latin American countries. My boss is from Venezuela and refuses to go back there, it's so dangerous now. At least in Mexico you don't have to always be watching your back. I'd say the best places to go in terms of security are probably Cabo, Mayan Riviera, Cancun, and Cozumel. Avoid the northern border states, Mexico city, Puerto Vallarta, Acapulco, and southern states like Chiapas and Oaxaca.
General tourism rules apply here as well. If you drive, keep an eye out if you're being followed. I wouldn't recommend driving in the cities at all. Use only clearly licensed taxis. Don't just wander around alone. Don't carry a lot of cash on you. Don't wear any jewelry or expensive clothing. If you must bring a cell phone with you, grab the cheapest and crappiest one you can find. Just like here, muggers only want higher end smartphones. Phone theft is becoming a big problem down there. Stick to the resort area. If you must get drunk, do so on the resort. A lot of tourists get themselves beaten or killed mouthing off to the locals in the clubs where machismo runs high. If you do get into trouble, don't count on the cops to bail you out either. Gringos aren't well liked south of the Rio Grande. Just be polite, keep your mouth shut, and try not to make yourself a target. And if you do get into trouble, just give them what they want and hope they go away.