So other than shooting dark rides at the world, what else do you use a prime lens for?
At one time zoom lenses were considered bad. They were not made very well. They were very soft and looked down up by the "pro" and high end amerture photographers. Prime lenses were IT! They've been around A LOT longer than zooms for one and they are VERY sharp.
Some people still only use prime lenses and forgo zooms altogether. If you look at Gdad's post about his upcoming trip to New Orleans, he lists what lenses he is planning on bringing and they are all prime lenses.
I'll many times put my 30mm or 50mm lens on my camera and use only that for a few days. I'll shoot the kids outside or around the house. With natural light and with a flash.
When I want to take portraits of the kids I'll use the 50mm f/1.8.
Now just because the lens can open up all the way to f/1.8 doesn't mean you HAVE to only use it wide open. Lenses are sharper when stopped down a bit. So my 50mm f/1.8 while pretty sharp wide open at f/1.8, is even sharper from about f/2.8 to f/11. It is (so long as my focus is spot on) razor sharp at f/5.6:
Here is one I always like to use as an example. I took this for x-mas 2006. Nikon D50 with the 50mm f/1.8 lens and SB-600 flash with diffuser. ISO 400, f/5.6, 1/60th shutter:
Also the full MACRO lenses are prime lenses. Typically f/2.8 with a full 1:1 ratio.
You can use a Prime lens for the same things you would use a zoom lens, except your feet now become your zoom.