Hard to describe, here is a video of what a wobble looks like:
Sometimes its so bad that they can't aim to strike.
The wobble looks a little goofy but as long as they still eat ok the wobble really is no big deal. I own 4 BP's with a spider gene in them and they all grew out of their wobbles. I've heard some keep the wobbles and I've heard rarely that they get worse with age.
One more spider trait is that they tend to be more curious and outgoing than the average BP.