You mean like the lady in New Brunswick, Canada and the young fellow in Idaho who are both growing lemon trees? A LOT of people on this site take part in what is widely known as "pushing the zone". About this time of year you'll find a lot of discussion about it on, say, the Tropicals forum where folks up north growing tropical stuff are discussing how they overwinter their plants.
But we've also had a fairly in-depth discussion about how the USDA zones really aren't that applicable to home gardens anyway, since they were originally intended as guidelines for farmers. I'll see if I can find it and post a link for you.
Our house in Utah was zone 5 in the front yard (facing north) but against the south facing wall in the back yard I had things stay green through winter, like Nasturtiums. So more like zone 7.
Then you get a plant tag on a transplant from a big box nursery that says "hardy in zones 4 to 9" and what that really means is "This plant will SURVIVE in those zones but it will really only do well in zone 6 and 7". (be careful what you buy at the big box stores, btw)
