No, duty is still charged for anything we import from the U.S. unless it meets certain rules (for example, if we visit the U.S. we are allowed to import items up to a limit based on number of days in the U.S., without paying duty on them) and technically, anything we buy from the U.S. without having been there should be subject to duty. The free trade agreement did not change this (except possibly to make some of the limits more generous). When we receive mail-order goods from the U.S. without having to pay duty, really, we are getting off easy (maybe because an automated system didn't detect that the package contains a retail product, or maybe just because someone was lazy, had too many other duty goods to process, etc.). For me it seems to be a random thing - I always get USPS shipping and about 2/3 of the time I don't pay duty and the stuff just shows up at my door, but the other 1/3 of the time I get "caught" and need to pay.
Some companies, such as LL Bean, charge duty to Canadian customers as part of the order and pay it on our behalf. When I order from them, the box always comes right to my front door.
Stebby