My opinion is that most of the time, most code does not need commenting upon. But your public interfaces should always be commented. In my code what I intend to be public is generally fairly obvious - it is what you see comments next to. :-)

I explained my views in more detail in the thread starting at Re (tilly) 1: What you want and perl advocacy gone way wrong. (In that thread look for the post by IO, really.) I would also recommend The Pragmatic Programmer and Code Complete for two other books that offer good advice about the issues that commenting raises.