I thought I'd give an update on this, as a few years have passed, also there's loads available secondhand these days and someone might be having a think about one.
Firstly I should say I use this exclusively on the 1D4, so this may not apply to all, but I have had a ball with this lens and still use it as my main lens. I have no trouble using it with the 1.4 extender, full auto focus and, as I was informed elsewhere, I have a slooooooow auto focus with the 2 times convertor in live view mode, ok for stationary subjects.
Yes there is an amount of dust in the lens, but it would seem looking at the stuff for sale on the market, all lenses get dust in them, including prime lenses. So to conclude, would I recommend it...…………….yes I would, am I thinking of upgrading to something else...…...yes as a lot of my togging is done in poor light(dark forest is one location I go to a lot), so a faster lens is on my hunting list.