I have received information that 412.9750 MHz, NAC293 is being heard around the Boston, MA area. This frequency has been identified in the San Francisco area as being used by the Coast Guard as "NET 409".
Reports are that so far all traffic is encrypted P-25, and this frequency is new to the area.
These new UHF channels are part of a radio upgrade program for Coast Guard law enforcement and homeland security activity. But we still don't have a good handle on other frequencies that might be in use, so keep searching!
UPDATE - Bits and pieces of information continue to come in. First, the frequency of 413.0250 MHz, NAC293 has been heard active in the Southeast Florida area. It has been encrypted full time so positive ID has not been made. From a separate source, I have confirmed that Coast Guard assets in the Miami / Ft. Lauderdale area do indeed have UHF radios installed in them. They have been reported as using "NET 411", but no one has yet confirmed the frequency. Does NET 411 = 413.0250 MHz? We shall see if anyone can connect these pieces.