Found an interesting article on modifications to the USDA plant zone map of 1990. Here in the Tampa Bay area we used to be in zone 9b and now they are calling it zone 10. Depending on where you are there may be some gradual changes in what grows and flowers and when.
http://www.ahs.org/publications/the_american_gardener/pdf/0305/USDA_Map_pp_30-35.pdf
Thanks, I was looking for that just yesterday. :)