I came across this site quite serendipitously, however I am glad I found it! I have been a "cracker" of joints for practically as long as I can remember. I couldn't give a specific age, but I am pretty sure I was like maybe six or seven when I started cracking my knuckles. From there, I went on to cracking my hands/wrists. That habit actually started to worry me when I started having problems with joint pain in my wrists, but I came to find out that I simply needed an ergonomic keyboard (I am a legal secretary and type a lot!) So the cracking of my joints wasn't hurting me - it actually probably helps, as it seems to get rid of my aches and pains. Recently, I started noticing I can crack my sternum if I stretch just right, which was madly disconcerting at first. I think what was most disconcerting was not so much the odd noise it made, but the fact that it felt so good and eased so much tension. While I am sure this is mental, it I truly believe my cracking has some sort of therapeutic effect. Anyway, I also crack my back and my toes, and due to some issues I have with hypermobility, I can crack me knees. (Although that doesn't always feel so good!)
It is great to finally see there are other people out there that are crackers - haha, that sounds rather strange, let's say "poppers". While I don't think of it much, and just do it subconsciously, it is sort of fun to see why others' think they do it, and their reasons why they like it, etc. Very different - yet cool - site!