Associate
If your current system does what you want it to, keep it until it doesn't. I'm going for SB, because my current pc is a buggy laptop, and four years old. I'll probably not go for Ivybridge, or even Haswell or Rockwell...but whatever comes out the year after I leave Uni (2015) I'll take, unless something breaks first.
If it's not broke, don't fix it.
If it's not broke, don't fix it.