I've found various opinions, and personally feel the EF 85 1.8 suffers with a bit too much purple fringing in back lighted situations. But, it's not
an expensive lens, so shouldn't expect perfection.
I've owned and used the Canon 85mm 1.8 for a little over a year now, and in my experience with it, it has performed almost flawlessly. I don't usually shoot in extreme back-lit situations, but it has handled strong contrasts (like tree branches and telephone wires against a bright sky) with minimal problems. In fact in my post-processing, the 85 1.8 generally requires almost no chromatic aberation correction at all. It's the best of all my lenses in this regard.
The Ultrasonic motor makes for fast and quiet focusing and build quality is as good as a non-L Canon lens is going to get. Sharpness is very high right into the corners on my 5D and distortion is almost non-existent. Great bokeh if you use it at large apertures too. Personally, I shoot mainly for good detail and large depth of field. This lens has not disappointed me yet.
As dang stated, it's not that expensive a lens and that along with its high performance makes it one of Canon's great values. If you plan to work in and around that focal length, I highly recommend it.
If interested, here is a sample of a black and white image taken with the 85/1.8:
http://www.pbase.com/ken_bat/image/100446090Ken