when using gels, what does the "smiley effect" has to do with it. And
what is the smiley effect. What is it all about.

                            Ted.

This affects polyacrylamide gels more than agarose.  The effect seen
is that the contents of the outer wells on a plate run at a different
rate from the inner ones, thus the dye markers used adopt a concave
"smile" or "frown shape. This hampers direct lane-to-lane comparison
of mobility and so it is routine practice not to use the outer wells
for this reason.

I'm not sure if the physical reason for this effect is well understood
(at least, it isn't by me), but it may relate to gel overheating due
either to too high a running voltage, wrong buffer concentrations, or
poor temperature control during running.

There are actually two kinds of smileys which happen.  Individual
bands can smile or frown for a variety of reasons, or the outer bands
can smile by running slower than the center.
The individual band smiling or frowning is often caused by running at
too high a voltage for your gel/buffer system.  With protein gels,
secondary structure can cause aberrations, particularly if your sample
contains serum or high concentrations of albumin.  Sample containing
lanes adjacent to empty lanes will also spread out, due to the
different salt concentration between the two lanes.  To remedy this,
just add sample buffer to the empty lane.
Whole gel smiling is due to overheating of the gel.  Just as the
resistance of a wire increases upon heating, so will a gel pass less
current through the hotter edges of a agarose or acrylamide gel.  If
you set your gel rig to constant current mode, you can actually watch
the voltage increase through the run, and the effect is more
pronounced if you add less buffer.  Modern image analysis software
usually has a provision for "smile correction".

http://www.ruf.rice.edu/~bioslabs/studies/sds-page/gelgoofs/misc.html