I've recently started making a serious effort to improve my hip flexibility too. For years I only stretched out 2/3 times a week before each training session, but for the past month I've been stretching twice a day and can see some progress. I can get to the invisible collar without any problems, so my flexibility can't be that bad!
On a slightly different note, my neck is very flexible (immune to neck cranks, and I can roll back on my neck so that my knees touch my shoulder). Anyone consider a flexible neck an advantage to JJ?