I thought the lens on the XL1-S had been "fixed" , but I still read posts on forums that say it has a focus drift problem. Is this true? Do most lenses work and some don't?

I think you are referring to focus hunting. To my knowledge this
still happens. Problem goes away if you switch to manual focus.

<<<-- Originally posted by Rob Lohman : I think you are referring to focus hunting. To my knowledge this
still happens. Problem goes away if you switch to manual focus. -->>>

I thought there was still some "back focus" issues with the lens or something.

The back focus issue was really limited to the original XL1 and was fixed via a firmware update by sending the camera and lens to Canon. However, any camera, prosumer or professional, with interchangeable lenses, can have a problem with back focus. Most pro lenses have a back focus adjustment, the AF lenses with XL mount do not have a back focus adjustment. If the back focus goes out, it's a trip to Canon for a fix. The two manual focus XL mount lenses have a back focus adjustment, like the pro lenses. Why don't the XL AF lenses have a back focus adjustment? Cost. Pro lenses start at what an XL1 outfit costs.