Lenses made for film cameras are not always optimal for digital cameras, or at least the theory goes. One contributor on Rangefinder Forum did an interesting comparison of four different 50mm lenses on the Epson R-D1, a digital rangefinder camera which takes lenses made for the Leica M mount.
The lenses were Cosina Voigtlander Nokton 50mm f1.5, Canon 50mm f1.4, Canon 50mm f1.2 and Canon 50mm f0.95. In most cases, the Canon 0.95 was the best, in my eyes and given the conditions of the test. This is quite astonishing for a lens first marketed in 1961.
I'd be quite pleased to have the R-D1 as a digital camera. It makes nice images, it's b&w mode is remarkable, and it (mostly) meets my requirements for camera design. That said, it is not inexpensive, even if you can get a refurb directly from Epson at roughly 50% off. In addition, Epson QC and customer support for the R-D1 is problematic.
So this proves I'm not totally anti-digital. If money were no object, I'd have an R-D1 and some nice Canon ... or Leica ... or Zeiss glass.