You haven't lived until you have hit an unexpected and unannounced patch of 0.05. (There is actually no such thing as Nil Braking Action - there is always some retardation - hence the 0.05).
The closest that I ever came to going aux vaches was one night at JFK. We were over the grass at the end of 31R but luckily the nosewheel was still (just) on the tarmac.
On another occasion, I landed at NUE one night in a snow storm off a CAT II approach just a few minutes after a 727 who had landed without a problem. The BA was given as 0.26 which was fine for us but it wasn't. We had about 100 feet to spare at the end of the runway. The moral to that story is that a BA is only good at the time the man takes the reading with his Mu meter. Two minutes later, it can be totally different.
I'm not sure how many airlfields nowadays give accurate readings for the taxiways. I landed happily at GOT one night with no problem but we started Scottish country dancing on the rather large ramp taxiing in. I think we were doing an eightsome reel when I finally manage to stop further proceedings.