> I have seen it everywhere (pull all unused output lines to 5
> volts). OK what
> if you dont do this? I have one curcuit that seemed to work fine and I did
> not pull the outputs up.

        CMOS doesn't like having floating inputs since the inputs are very high
impedance. Current flowing close to those pins could easily get the inputs
switching back and forth, creating a ton of unwanted oscillations which
could couple into other parts of the chip (and circuit) wreaking havoc with
your design. Now, having said all of this, I have also built prototypes that
worked fine with floating inputs. The biggest problem is when this problem
appears, it is very difficult to pin the symptoms to this problem. TTYL