I used cheap brake fluid at my first track day which boiled after the first session, but I wasn't smart enough to realise this and kept doing laps until my brake pedal sunk to the floor. Its taken around 8mths to have the problem fixed and around $3,000 worth of fixing/upgrades.
Its all good though, I learnt heaps, I did some major upgrades which -should- prevent this from every happening again whilst improving my car dramatically (on the track).