An interesting article just appeared in Aviation Ebrief:
"Holland's trial of Mode-S transponders led to a requirement that all
aircraft operating within Dutch airspace be equipped with the
transponders. However, the ATC system was overwhelmed by data from the
Mode-S transponders, and now all aircraft flying below 1,200 feet are
required to keep the transponders on standby."

Here's a link to the full article:
http://www.ainonline.com/news/single...le-in-holland/

I wonder how much testing and simulation has been done for busy US
terminal areas?

Charlie