Summary: I have this on my camera almost ALL the time now, it is my go to prime. I had the 50 mm, I hated it, I mean I loved the photos but I was always too close and indoors forget it I couldn't get anything more than a persons face in the frame. Beautiful bokeh, I'll leave the tech reviews to the experts.
Summary: This lens is great. It's my first venture into more expensive glass - yes, I know there's much better and much more expensive glass than this - and it turns out great color and excellent detail every time.
Summary: I have used this lens for a while since I can't afford the 1.4L version. It is a little noisy, but not as bad as some say. People make it sound like it's an X-1 breaking the sound barrier when it focuses, for goodness sakes. It takes clean, sharp images and the focal length is great.
Summary: An essential piece of kit. I have never really liked zooms - even a cheap prime beats an L series zoom in my opinion, in terms of image quality. For example - try this lens against the 24-105 f4.0 L lens at 35mm - at f4 the images are quite obviously different in quality - the cheaper 35mm beats it...
Pros: 1) cheap, 2) reliable, 3) light and compact
Cons: 1) slowish and noisy focus, 2) not sharp at f2.0 - you need to shoot at f2.8 and up, 3) colors are slightly washed out and grey looking - not much contrast on this lens.
Summary: I bought this lens because I wanted a good, fast prime lens for indoor use on my 50D. I also own the EF 50mm f/1.4 which I love, but indoors I find it less useful due to the crop frame sensor of the 50D.
Summary: This lens has seen renewed interest as it becomes pretty close to a normal lens ( 56mm equiv. ) on Canon's smaller sensor DSLRs. More than acceptable quality wide open & excellent quality at mid apertures makes this fast & relatively cheap lens very attractive to amateur photographers.