For folks who's reception conditions call for a preamp, it may appear to be a cure all. However, if you use the wrong preamp, in strong signal conditions, you risk overloading the preamp which will produce interference inside the amplifier, making for less reliable reception.
When faced with a mix of strong and weak signals, I'd suggest using a 'high-input' preamplifier. Examples: Antennacraft 10G201, 10G221 & RCA TVPRAMP1R.
http://forum.tvfool.com/showthread.php?t=13646