Zones overdue for another shift?

[TerdalFarm]

I just found this press release from the City University of New York in which a faculty person says that zones have shifted upward (warmer) by a half zone for about 1/3 of the continental US just since the last USDA map. That "old" map used data through 2005.
http://www1.ccny.cuny.edu/advancement/n ... I.facebook

After my Zone 8 winter last year, it makes sense, unless I think back to the zone 5 winter the previous year... .

[Jubaea]

All it takes is one bad year to make any of the maps irrelevent for long term culture of plants in borderline areas. I don't think the old data should be dismissed or else many people will be disappointed. What I think would be more usefull is the average frequency of different ultimate low temberatures. It is one think if your zone 8 shrub dies in a zone 5 equivlent freeze and another if your 30 foot tall tree dies.