i crack EVERYTHING, and frequently. knuckles, neck, shoulders, back (upper, mid, and lower), hips, knees, ankles and toes. i was actively attending a chiropractor from about the age for 4 through my late teens... now i go about 2-3 times a year as i feel i need it.
i did at one point try and stop, but found it more frustrating and felt tension and aches in my joints within about 2-3 days. i didn't see a point in not doing it, and have experienced nothing adverse from doing so.