Basically, I found out thursday that some of my code (that had to be designed long before all the requirements were known and thus wasn't well engineered code) needed major modifications to work with a new file format and it needed to work with that format by today (or I'd have to come in saturday to manually do it's work). I had to entirely rewrite the subsystem because hacking it to work wasn't really possible. It's now properly engineered, but needs several more layers to be as functional as the previous library I had written. Luckily, the program that was needed only required the base level of functionality from the library.
It was an interesting experience to be coding at 4AM and then find a complete lack of caffiene in the house =-/ Oh well, I worked much better after some sleep anyways. It cost me was a few points in various classes that I missed because of the sleep, but I think it was worth it to finish it 'early' so others(users of the program) might be able to avoid overtime if they want and I really didn't want to work on saturday (might still have to, but hopefully the program is bug free enough for now).