There's nothing wrong with South Beach, and I wouldn't let the comments so far keep you away.
I've lived in Miami since 1971, and I go to South Beach a couple of times a month...usually either for the beach itself, or to eat dinner. I also worked as a cop here for 25 years. Here are my impressions on the topics raised so far.
Body Parts
If you are offended by topless bathing, don't go to the nude beach. If you are offended by skimpy and outrageously-packaged bikinis, you might want to avoid the state of Florida altogether.
Drugs
The fact that a girl is six feet tall, thin, and incredibly beautiful does not make her a drug addict. She might be...but more likely, she's just your average supermodel. I've seen a lot of people drinking on South Beach, but I've never seen anyone using drugs. I'm sure some do -- some do everywhere -- but you won't see them lying in the street here like you do in some European cities.
Driving 
Wolfpack Fan is right - the traffic is bad. BAD. It's not so much that there is a huge
volume of traffic (we have a fraction of the traffic of Atlanta, for example). The problem here is the
drivers.
About 40% of our drivers here are tourists who a)don't know where they are, b) don't know where they are going, c) don't know how to get from where they don't know they are to where they don't know they're going, AND (not or) d) are not good drivers in the first place. This group is why you'll see a lot of bumper stickers saying, "When I retire, I'm going to move North and DRIVE SLOW!" This is also the only group who are not armed.
About 40% of our drivers are recent immigrants -- many of them literally driving a car for the first time in their lives. Their average age seems to be about 78. They're doing the best they can, but they can be exciting at times.
The other 20% are the more or less normal drivers, and they will display the full range of driving skill that any other population would display -- some good, some bad.
There are some funny driving practices that are common in Miami, but I'll spare you. Dave Barry does it better anyway. But suffice to say, Miami is an
amusing place to drive!
Difficult driving is a given, and road rage is a possibliity. South Florida drivers actually are not nearly as aggressive as say, Boston or New York drivers. The problem here is not aggression -- it's lack of skill.
We don't really have gun battles in the street, but you'll sometimes see someone rudely cut off. I don't do that, but most of the time when I see it, I
understand why it happened.
