The ratings only show what frequency it officially can support or is tested to. You don't have to use it all up, and may not be able to, that's part of the game in OC'ing. If you want to overclock, then I would get something higher than 3200.
But more importantly on an AMD board, you'll get more use out of the Enhanced Bandwidth than actual clock speeds that Intel chips like. OZC's EB 3500 or 3700 would be GREAT for your system.
"The motherboard is reported to handle up to PC3200 but I've heard people running PC3700."
The motherboard only officially supports those speeds. It's up to you to find others that are using it to see if they have problems or not, then decide. IMO, it'll take what you throw at it, but it's so new, I've heard very little thus far. It's rare when you hear a board-maker that officially supports anything BUT 3200. But, you can go to the memory maker and see what they're compatible with...and that's what I'd do. You may never get a board maker to say they encourage overclocking (but yet they give you all the tools to do so).
"Are they actually running PC3700 or are they running PC3200 overclocked to PC3700?"
They're running PC3700, or they'd say PC3200 at so-and-so speed.