This, and the Kodak Ektagraphic 50mm f1.2 projection lens, is one of the fastest projection lenses I have. I haven't used the Kodak version much, but I really like the Kowa. Most projection lenses are made for the 16mm projectors, but all of them seem to cover the APS-C sensor just fine.
The super thin depth of field of this f1.2 lens allows one to achieve some creative pictures which is not possible with the kit lens. The only downside is that aperture can not be controlled, and that it was hard to make it focus to infinity, even on the NEX, as the back of the lens is very close to the sensor. I love doing close ups with this lens.
Petals in the rain -- NEX-5 & Kowa Super-Promina 50mm f1.2. Click for larger.
Bausch & Lomb Super Cinephor 120mm f1.9 Project Lens
This is the fastest telephoto projection lens I have. The image quality is good, but the bokeh is messy and less than satisfying, but when you need a fast lens with good reach that doesn't cost an arm and a leg, this lens will do it for you.
Fall Leaves -- NEX-5N & B&L Super Cinephor 120mm f1.9. Click for larger.
In summary, projection and enlarging lenses are two of the cheapest ways to get high quality lenses. Projection lenses for low light and shallow depth of field, and enlarging lenses for insane flat field sharpness with aperture control. Both type of lenses need a focus helicoid to make them focus to infinity (or focus at all) but you will find the images you make with them will be worthwhile.