I'm not a huge fan of labels, either, because I dislike the "all or nothing" approach that labels encourage. Am I "AP" simply because I breastfed? Or am I "mainstream" because my baby slept in a crib?
I have to say that many of the parenting practices those above have described as "mainstream" are not ones that I encounter on a regular basis, especially spanking and CIO. I do not know any parents who used CIO a la "Mad About You." When my dd was born, I knew nothing about CIO/non-CIO issues, yet if my baby cried upon being put to bed, or in the middle of the night, we held and rocked and sang until she fell asleep. We just figured that's what you do with a baby! I agree with Amywillo that CIO is more of a sleep training issue, and I have yet to meet a parent who has truly let a baby scream herself to sleep. And I have a few very "mainstream" friends who would never, ever spank their children.
I think the one I see most is the whole "baby container" thing...you know, those babies who are always IN something, like a bucket, a stroller, a swing, etc. Sure, I used a stroller and had a bucket carseat, but I didn't treat those things like they were part of the baby herself! If I brought dd into someone's house in the seat, it was because she was asleep, and I'd take her out as soon as she woke up (and often before that, risking waking her, because I hated leaving her in it!), whereas I've seen babies who are just left in those things all the time, like the seat is part of the baby!
I love the way Piglet68 put it, that it is the attitude behind your choice rather than the choice itself, that if you choose something because it is what "everyone else does," rather than because it works for your family, that makes you "mainstream." I have met many, many parents who just follow the "Babies R Us" style of parenting, as I like to call it - the swing, the stroller, the bucket, the playpen, the stroller bar toy that every other kid has...you know what I mean. What makes me think of someone as mainstream is when it is clear that the person put little thought behind the choices she made (or he made) for her children, or worse, didn't even realize that there WERE choices. I actually commented to someone recently that her unborn baby might not need those cutesy little Pooh pacifiers she was buying and she looked at me with an utterly confused look on her face...