We just returned from a week in Myrtle Beach. I don't know where the poster in that other thread heard that it is getting run down, if anything it looked even better than when we were last there in 2001. And as far as safety, we stayed in the 6000 block of N. Ocean Blvd. which is pretty close to most of the restaurants and attractions and we never felt the least bit unsafe, not even once. I picked up the local paper in our hotel everyday and as I read the police blotter, I noticed that most of the crime in MB seems to be either domestic problems between people who know each other or situations where someone ventured into an obviously questionable area and did something stupid like carry a big wad of money in their shirt pocket. Sure, there are sections of Kings Hwy. such as in Surfside Beach that look like their best days may be behind them, but even there we didn't feel threatened in any way.
Honestly, I wouldn't worry about it. Stay in a nice, well kept area, avoid strangers, don't flash money, credit cards, jewelry, etc. around and don't go into places like public parks or seedy looking bars and you should be perfectly fine. Same advice one would give someone traveling anywhere in the US.