I don't know what the numbers are, but I are one. I've been turning wrenches as long as I've been flying (maybe a tad longer). It's kept me employed during furloughs, downsizes, and other times, and it's been a foot in the door at others. It's inconsequential if looking toward an airline job, but it's served me well, and I've always encouraged others to get maintenance experience and certification.

Note that much like pilot certificates, having the mechanic certificate is no guarantee of skill, judgement, or ability. There are a lot of "A&P" mechanics out there whom I wouldn't let touch a popsicle stick, let alone an aircraft. The same rings true for pilots. Unlike pilots, however, there are a lot of practicing mechanics out there who aren't certified, who are skilled, knowledgeable, and able. These work as apprentices or assistants, and I've met quite a few who did far better work than many practicing A&Ps in the field.