Roger Johansson's rant against the three column CSS article
on A List Apart expresses pretty much anything I'd like to say about the subject.
Yes there are some valid uses for this, a navigation block springs to mind, but I'm afraid most of the time we'll be forced to read awkward pagedesigns that haven't accounted for our particular screensize.
On another note I've got to get me one of those puzzles:
Found via Unshelved