I did, when they asked me to go in at 6am over christmas. I did it twice on the same day. There was a TV program where a guy did this. He ended up being quite bored in the middle, and couldn't really get the hang of it. That said, I think he did it for 2 weeks, which isn't enough time to adjust. I'd not do it. I'd like to try staying up 24+ hours, so that I can correct my sleeping pattern though. Wake up at 11am, stay up a whole day, then go to bed at maybe 8pm, so that gives me a little extra to catch up. Hopefully I'd correct to waking up around 8. Knowing me, I'll just f**k it up again.