Was working as a research assistant for my university's NLP department. Had a script to process a few gigabytes of text, knew it was going to take all night, so I ran it before I left. The code was still rattling around in my head on the bus and I realized I had made a mistake that would cause the output to be useless. Opened up JuiceSSH on my phone, logged into the server, fixed the code and ran the script, next day everything was peachy.