Just a couple clarifications, its not so much smoothing airflow, but intentionally giving a bit of turbulence to EVEN out the airflow across the MAF opening so the readings are consistant, and it is most critical at low engine speeds, idle being the most obvious. Some cars run fine without it, some won't run at all without it, to everything in-between.
Some past posts on the subject...
http://www.contour.org/ceg-vb/showthread.php?t=47884&highlight=MAF+screen
http://www.contour.org/ceg-vb/showthread.php?t=28012&highlight=MAF+screen
And fwiw, I'd be interested in seeing the link Brett found that you mentioned. I don't believe I've seen the post in question, but I have a feeling its a guy I used to work with that spent some time in MAF design at Ford.