--though sporadic--of neuropathic symptoms resulting from too much B6 in the serum (referred to as pyridoxine intoxication). Usually, these have occurred in those who have really megadosed--on the order of 200mg up to a gram each day.

As Mrs. D notes, though, this seems to be associated with a genetic inability to chemically reduce pyridoxine to the active pyridoxal form. This genetic profile seems to be associated more with certain other conditions (autism for one), although certainly no causality has been established yet. For those who suspect this, taking the already activated P-5-P form of B6 seems to help; to my knowledge, there have been no reports of these symptoms on large doses of P-5-P.

The Useful Websites section of our Vitamins/Minerals/Supplements Board has a significant section about this:

http://neurotalk.psychcentral.com/thread30724.html