I did this for a couple of months at my university, having failed to secure accommodation at the end of a rental period. Slept variously in an electron microscopy suite, a darkroom, and a rarely used bathroom. Wasn't too bad, though there was the omnipresent fear of campus security twigging on. As this was in London I saved quite a decent wad of cash in rent. Wouldn't do it again though unless I was particularly desperate.