I'm Diamond on NA/SEA and high Platinum on KR. I've played around 180~ games on KR so far and it's a whole different experience, everyone is just so much better. I found myself losing a lot of games early on because I was relying on a lot of stuff that just doesn't work against attentive and generally good players.
Playing on the Korean server has actually done more for my SC2 skill than most of my games played on NA and SEA--it's an absolute must to people who want to get better fast.
As far as pings go it really depends on your ISP to be honest, I've got Bigpond cable and I actually get the same ping to SEA as I do to KR, which are both better than my ping to NA--however using my brother's Optus cable he gets a fairly bad ping to Korea but gets good pings to SEA and NA.
Even the smallest donations help keep sc2sea running! All donations go towards helping our site run including our monthly server hosting fees and sc2sea sponsored community tournaments we host. Find out more here.