ditto to what matt said. if you really feel that you'll be frusterated with the negatives of the 1.8 II, then just get the 1.4 version. I just got a 50mm 1.8 II because i needed something really cheap for a trip I'm taking. Here's what i think so far:
Build Quality/usability: Bad. Real bad. the build quality is near horrible, with a very very plasticky feel. It's almost too light, and feels like if you dont hold it right you'll crush it. It's useable, but gets a little annoying...the manual focus ring is a tiny little thing at the front of the lens, and is pretty impractical. the lens also doesnt have a focus scale, which can come in very handy.
Autofocus: It's decently fast, but not really fast. It's also kinda loud, which can be bad in certain situations. Certainly not as fast and silent as ultrasonic lenses like the 50mm 1.4, but still ok for most situations.
Optical Quality: very good. at f/1.8, you can usually get sharp images (you have to watch out because the DoF can be pretty shallow), and at f2.5 and above the images are razor sharp. there isn't much CA except at f1.8 and f2, but it's not bad, just a little glowy/low contrast. the bokeh is a little dissapointing, but certainly better than you might expect for a lens with only 5 aperture blades. out of focus grass looks pretty bad, but that's a pretty tough test for any lens.
Even after looking at the downsides I realized that the low price (i got mine barely used for $58 ) easily made up for them.