One full week. That's how long it took me to recover from COSSFEST 2009. Mainly because of all the effort that went into setting up the event. The Friday night dinner/karaoke/drink-a-thon didn't help any either.
As one of the planners, I saw the inner workings of the event. I saw a number of things that just fell together right, and a few that didn't work at all. Luckily most of the latter type were not visible to the attendees, and have been identified as issues to address next year.