I use the headphone jack moderately and have had no issues with it so far, knock on wood.
This was a pretty big issue with the original Droid though, as its design seemed to be perfect for making the jack "wiggly". Good thing the whole jack is now "enclosed" on the X.
Btw, this is a hardware defect and should be covered in your warranty (I got a new D1 from VZW because of this same issue).