Due to the fact that JKR almost admitted that the fans got it right with Regulus, even this soon, what I want to know is why didn't he destroy the locket right away?
We all have our theories on what motive he had (redeem himself to his brother, just couldn't follow through, etc) but I find it interesting that he left such a valuable part of Lord Voldemort(oh for heaven's sake, stop cringing) in a desk.