Last fall between 7:30 AM and 9:00 AM in PDX, the city police set up orange cones along with large orange signs saying "Traffic Enforcement Ahead".
They gave out 29 citations and 33 warning to bicyclists and 15 citations and 4 warnings to cars, and made one DUII arrest.
It wasn't a speed trap, rather a 4 way stop signed intersection. However, again despite fair warning, plenty of people just plowed through the stop signs.
-r