Upload & Sell: Off
It focuses as quickly and accurately as my 70-200 mkII. I can rely on it for street photography at night, travel photography during the day, portrait sessions, events, and just about everywhere. It is a phenomenal focal length for me personally because I am inept at framing wide angle lenses and 35mm feels JUST right for most city and landscapes that I shoot. It works great for full body portraits, environmental portraits, and even upper body portraits. Hell, if I had to choose a single lens to travel the world with it would be the 35L.
On top of all of that bag of usefullness, it renders images incredibly distinctively and in a way that I personally believe is very close to leica/zeiss glass and unlike any other Canon lens I have owned. The only thing that I believe the lens could benefit from is weather sealing. I was thinking about whether or not I would ever upgrade to a mkII version if it came out but would be highly skeptical of canon's ability to maintain the character that this lens has in the mk II. Don't let the 100% comparisons to the sigma fool you this lens is SHARP wide open - where I use it 90% of the time - and has boat loads of contrast and excellent color. You are not buying a second rate lens if you pick up a 35L.
Here are a couple of photos I took last weekend. Haven't had enough time to perfect the editing etc. but it gives you an idea of rendering etc:
and one from Honolulu for funzies:
This was the first prime I ever used that really changed the way I approached photography. Give yourself the opportunity to at least try a 35L. It will not let you down.
Edit: I have also had enough experiences with sigma to know better than to buy one of their products again. Even if they sorted the focusing inadequacies out, I still don't have faith in their mechanical quality.