The currently pending patent reform bill would create an expanded prior user defense to patent infringement. Under the proposal, an accused infringer would not be liable for infringement if it had been commercially using the invention at least one year before the patent application filing date. The defense would extend to affiliates and assigns.
However, an invention that in commercial use more than one year before the filing date would usually be found unpatentable as anticipated. Can you provide example situations where prior user rights might be important?