Yes, have done many times. I don't think there's anything "supernatural" involved (if such things work, they work for anybody, which means they're natural and not supernatural - I pretty much reject the term). I don't subscribe to "oooooo...scary...mysterious" beliefs about any of this stuff. It just is or it isn't. Some members of my family have had abilities that were pretty much matter-of-fact. For instance, back when they didn't have telephones (or electricity, or running water until the late 50's) my grandpa would always know when family was coming to visit...he'd just tell his mom, or later, my grandma, "We're going to have company for lunch" and she'd make extra. He had no way of knowing because sometimes family would just stop by and have no way to call ahead. Nothing odd or spooky or mysterious...just something he could do.
I don't consider myself terribly gullible. I'm basically agnostic about all of it, but am often willing to give it a try just in case.
RE:karma - you can't really say that we've imported the idea of karma from Eastern religions. Our idea of 'karma'...that our actions will either be rewarded or come back to bite us in the ass *in this life* (that's not karma, that's common sense)...is NOT the same as the idea of karma in Eastern religions, which, as I understand it, deals mostly with reincarnation. At most, we've imported the word, not the concept.
RE:witchcraft - the main problem with the term is that, as Europeans went out to 'discover' and 'study' other cultures, whenever they came across a culture that believed that people could use some sort of supernatural force (usually through emotion) to cause harm to others, they'd translate that as 'witchcraft'. When the Christian god is involved they call it 'miracles' ...when other gods were involved they call it 'gullibility and coincidence' In some African groups, the person may not even know that they are doing it...many 'witches' (again with the translation) in those cultures are unaware that they're witches.
Anthropology now often has to add a seperate note in the definition that this is very different from modern neopagan witchcraft.
I think many many religions (especially fundamentalist Christianity) uses what I consider folk magic (edited to add:that 'burying a saint upside down to sell your house' thing is a good example of this - it's not a Christian doctrine thing *at all*)...when a whole church 'prays real hard' for certain outcomes (a favorable outcome in a legal case, certain politicians to get elected, people to be healed), they are directing *emotional energy* to effect a certain outcome...which anthropology defines as witchcraft (although I'd be amazed if you could find an anthropologist [besides me] who'd call it that...we're pretty myopic when it comes to western culture). Folk magic is a component that may be present or absent in any religion.
JWs in general are one of the groups where anything that smells of folk-magic-y influence is avoided like the plague. Even their group prayers are dry and seem to be without that.