I'm not sure what happened to the post on the $750 24-105mm L IS USM, but I bought one and it shipped immediately showing up at my door 2 days after. The seller was BigValueInc and there was some debate as to whether the lenses were really new, whether they were a Canon retailer and if the lens was under USA warranty. They are not a Canon Authorized retailer (there's a PDF if you google it and they're not on it).
The box came and it was a white box with no warranty card though the lens appeared brand new. It came with the lens pouch, the front/end caps and lens hood as you would expect. I emailed them and asked about the white box and missing warranty card and they sent me the reply below. I also did go to Canon's website and started a warranty claim and they show it as under warranty (I canceled the claim before submitting final).
This is there explanation...
Thank you for your email. I am very sorry for any confusion this may have caused. This item was removed from a kit box that included the body of the camera. To sell this item at the price we do, we put the lens in a separate box and sold the item. It is brand new and never been used. This item is covered under US warranty and you can register the item by the Serial number. If you would like to return the item, I can set that up for you as well.