once gone sleepless for two consecutive nights, or rather 48 hours... (the nights were distorted as it was during travelling...)
At uni we (/I) decided to have a 24 hour party on the night before every England game during the 2002 World Cup. Not particularly crazy parties, more tests of endurance (and come 4am, coffee drinking ability...) By the time we played Nigeria I could only see green and white dots running around the screen... Good times...
Mine is three hours. I had to do work on my thesis. It's really hard when you lack sleep. Your brain feels empty..