Is a Canon USA warranty card included?
Previously my Canon kit included warranty cards for both the camera body and the kit lens. I passed the card along to the buyer when I sold the lens new and unused. So a warranty card should be available and other sellers include one (though they charge more).Lens buying seems so hit and miss that saving a little for a large risk without a Canon warranty might not be slick.
The warranty card means nothing if it is not purchased from an authorized dealer.
Unless you are a technical person, who actually follows all of the tests for lens, you feel no different.
p/s: is this lens noisy with the IS on? My lens was very noisy on the 20D body. Not yet try it on 5D.