Once again the point has been missed here. There's no questioning that the 50/1.4 is a better lens. Better in what respects and how much better in those respects and is the extra price justified for your purposes, are the questions. If you are on a budget and you want to take the sharpest pssible images, then the 50/1.8 is one of the best value lenses around.
Daniel's points are all valid, except the 'silliness' issue. (That's just plain silly, Daniel
). And I'm not clear what 'harsh highlights" mean. Perhaps you could explain that.
The more expensive lens usually tends to have better performance at maximum aperture, and the 50/1.4 is no exception here. If I were into shallow DoF photography, I'd pay the extra money and get the 50/1.4. However, most 35mm lenses tend to be sharpest at f8 and both
these lenses are no exception here. I doubt that the differences at f8 would be noticeable except at 200% enlargement on screen, representing a print size much larger than anyone would be likely to make from the 35mm format.
There's no doubt that the 50/1.8 is ridiculously light. When I picked up mine up from the shop, my first impression was that the lens elements had
to be plastic. I was assured they weren't.
But there's an advantage to lightness. This lens is always in my camera bag. It takes up next to no weight and little volume. However, because I've read reports that the lens can get damaged rolling around in a loosley packed bag that might bounce around on rough terrain, I keep it in a small 'bubble wrap' envelope, in the bag. (You seee, I was brought up to take care of my lenses
Lastly, when you buy a lens, you should beware of technology lust. I'm sure we all fall into the trap of buying the 'best' when we don't use or even need the best.
A 50mm prime is not the sort of lens I use often for my, mainly, landscape shots. It's very apparent to me, if you can't fill the frame with the conceived composition, then any resolution advantage a prime may have over a zoom is dissipated. My 50/1.8 essentially becomes a portrait lens when I need that. If portraiture with my 20D was my main activity, I'd definitely opt for the 50/1.4.
As it is, I don't need unused capital sitting in my camera bag 95% of the time. Nor am I interested in throwing away good money for the sake of camera/lens appearance, although I can understand that professionals need to impress their clients