A wobble is a genetic fault (for lack of a better word) that can be found in spider BP's and spider morph (eg bee's) it is a malfunction of sorts in their brains which can affect their motor skills. Some spiders don't show this at all but it can range to quite severe including a "corkscrewing" of the head. It tends to show more when the animal is stressed or excited (eg handling and feeding etc)
Most spiders/spider morphs live out full and happy lives, I think as long as they can feed it is not a problem.
Search youtube for spider wobbles, there are a lot of videos to illustrate what it is. It is not necessarily harmful to the BP but there are comments by people who don't understand who think it is very cruel and that the morph should be eradicated. A view that I highly disagree with.