If it were me I would trade down to a GTX670 and use the extra money on a nicer case and an SSD to run the O/S. Nobody *needs* the difference between a GTX670 and GTX680 - it's pure epeen. The GTX670 gives you 95% of the statistical performance, and in the real world you'll not notice the difference worthy of the increase in price. And nobody *needs* an SSD to run their operating system off, but it is one of the most impressive performance jumps one can make (if you've not done it before), and I will NEVER go back.
Also I would trade out the Corsair RAM for Samsung 30nm chips (with a small overclock on them) - I recently did this and couldn't be happier. The system feels faster, more stable and so forth. The old corsair RAM was Prime95 and Memtest stable, but never responded well and didn't play nicely with my CPU's IMC.
Also a GOOD 500watt PSU is more than capable of handling a maxed out OC on an i5 3570k and a GTX670. Better off getting a slightly lower powered PSU with a higher 80-plus rating and modular design for storing cables, which impeed airflow and thus overclocking potential (and component lifetime theoretically), which is why I suggest a bigger, nicer case with more airflow and cable storage room.
All that said, the build is wonderfully balanced as it stands, and you can't go wrong with it in it's current form. However, I think you can improve ever so slightly