I'm a SC native, lived in Columbia and Charleston, currently back in Columbia. First thing: everything you have ever heard about the 'good ol' boy' political system is true, in fact it's probably worse than you'd think. As long as you aren't actively in politics, that won't really affect you. Just don't think that getting anything changed is easy because it's not. BTDT.
The coast is cool, I echo spitfirebill on that one. The weather is (for the most part) fantastic. Winter there is like spring everywhere else, it might get in the 20's at night a few times but that's about it. In my 20 years there, it snowed 3 times and was gone in 48 hours or less. July and August are almost unbearable (heat, humidity) but the rest of the year is really nice. The drawbacks of the coast: sand gnats (called 'flying teeth' locally), no hills (10 feet is a big elevation change), too damn many tourists, hurricane season and real estate can get stupid expensive.
The Columbia area Midlands are boring. I'm here temporarily until I can find property in the Upstate (it's a long story). The upside: the scenery is really nice, autumn is BEAUTIFUL. Houses are cheap. Lake Murray is real close if you like watersports, other than that there's really not much else to do except drink. The weather is nice, it can get stinkin' hot in July/August like Charleston and around February it can get crappy wet/cold for a few weeks but otherwise pretty nice. Once in a while, there are 'ice storms' (sleet that freezes) and then it gets pretty nasty. The longest one I remember lasted a week. It will generally snow once a year and like Charleston it's usually gone in 48 hours. No hurricanes. The downside: as I said, it's boring. The further out of Columbia you go, the more boring it gets.
The Upstate is where I want to wind up, west of Greenville, maybe over toward Clemson. Real seasons, no hurricanes, it snows more than Columbia but it's still not bad. I like snow every so often but unlike Northern climes Upstate snow doesn't hang around for months and get slushy etc. I love mountain scenery. The mountain towns etc can be as boring as Columbia but there's a lot more nature stuff (hiking, etc) to do. Housing prices are reasonable.
Motorsports: Charleston is a wasteland. The one good local AX venue is gone. Savannah is the nearest track going south, then CMP going northeast. There's a good AX venue in Florence but Florence has to be the most boring place on the planet. Darlington has the big NASCAR track, I have never heard of any amateur motorsports there.
Ditto Columbia, the one good site went down because of University of SC politics (there's that good ol' boy system again). CMP is near Columbia, SCR-SCCA has a time trial program in place and the Sandblast Rally is held annually near Society Hill, about halfway between Columbia and Charleston, near Florence.
Greenville has the BMW plant and Michelin, both of them support amateur motorsports and there are hillclimbs put on by CCR-SCCA in that area and in North Carolina. I hear tell there's another CCR hillclimb event planned for northern Georgia, IIRC that will make a total of six for the hillclimb points series. Road Atlanta is reasonably nearby and the Atlanta area AXes are a daytrip, unlike Charleston etc.
If you are into dirt bikes or mountain bikes, there's a lot of places in the Upstate to ride as well as Georgia and North Carolina. If you are into those types of sports, let me warn you about red clay! If there's an event on red clay and it's raining, you are probably best off just curling up with a book in front of the fire. You can't even stand up on the stuff, let alone ride anything. It's hard on clothes too: I have some underwear that are permanently red stained. 
