Just received my Nikon refurbished 50mm f/1.8 lens today (along with a refurbished 24mm f/2.8) and had a chance to shoot a few with it. For a $100 lens, I have to say I am impressed. While the plastic barrel feels cheap (because it is), and the autofocus is noisy, I find the image quality to be very good. It auto-focusses rather quickly and with good precision, although occasionally it does miss in lower light.
This is a full-crop of a jpeg image taken today with this lens:
And a couple more from today: