As far as I know there's only been one long term (informal) study, where one guy cracked one hand and left the other, and there was no difference when he was in his 80s. The crack is just the sound of gas inside the joint moving around - it's not the sound of your bones scraping together or anything sinister like that. edit: just looked at the wiki page and there have actually been a few bigger studies but none have found any link between cracking and joint problems.
Yep, pretty much. That crack is not anything like bones smashing together; it's the rapid release of fluid from the joint when it is moved a certain way. You're not losing it either, because it slowly makes its way back in as well. No harm, no foul.
