@mt009,
Those are usually spam posts. A spammer selling, say, shoes, posts a picture of them and then tags a ton of semi-random people. He might be getting your name with auto completion or scouring a group or page for fans, who knows? You get tagged and so do the maximum on FB for tagging an individual image (
50 people or pages). Then someone acts to not only get themselves untagged, they report the image as spam. Enough people (how many is enough? I have no idea) report the image as spam and it's removed.
And that's it.