I WOULD NOT RECOMMEND ANYONE BUY THIS LENS FOR ANY PRICE, NO MATTER HOW TEMPTING.
In my opinion, this lens's price is way over inflated, due to it's fragile internal electronics.
I have this lens. I bought it used some years ago, still in great shape. Now, it's nothing more than a really expensive curiosity stuffed at the back of my drawer. As it's been said, it focuses electronically at a glacial speed, even in manual mode. The USM gave up without warning on me after 2 years owning it and an authorized canon repair center could do nothing for me, even after contacting Canon Europe, as spare parts are unavailable. They also said Japan wouldn't have parts for the lens. I even contacted Canon US to no avail. The motor is not compatible with any other lens like the 1.2 50 or 85. So, now I have a useless, non-working lens. If I could at least manually focus the lens, I wouldn't have minded nearly so much. I've since bought a 1.2 50 which is far better.