The first one I bought wasn't good at all - unacceptably soft wide open, sometimes back-focused, sometimes front-focused, sometimes didn't focus on anything at all, sometimes got it just right; completely unpredictable and thus useless (unless you like to maximize the element of surprise in your daily life). I then tried the Sigma equivalent, but it was far worse - I don't think I took one photo with it that was in focus (even though the camera thought it was). At that point I gave up on a 50mm 1.4 for my Canons and bought a Panasonic/Leica 25mm 1.4 for my Olympus OM-D - first rate in every way, like all the M43 primes I own (though not, of course, exactly a 1.4 equivalent). Encouraged by that, I tried another Canon 50mm 1.4 and, perhaps by chance, alighted on a copy that has never given me a problem. It may not be very sharp wide open (miles better than my first copy, though), but the bokeh is marvelous, especially if you get close to the subject (I've not yet seen anything like the rather harsh background in the photo Dustin's complaining about; I wouldn't want that either). So unless/until it breaks I'm happy enough with it. If Sigma or Canon were kind enough to provide improved updates, however....
(I've also owned the 50mm 1.8 and 50mm 2.5 macro but kept neither - don't like the bokeh on the former, and while the latter was very sharp and no slower or noisier to focus than a lot of Pentax lenses I was familiar with, I replaced it with the 100L macro as overall more useful.)