Harlequin, the Computar dL (dL stands for 'Diffraction Limited') series of lenses are very high quality but they have their problems too. Some, not all, suffer from separation and this can be hard to see if you are not used to looking for it. I don't think it's a problem with the 2.8/50 dL but it's certainly a problem with the 1.9/55 dL, in any case, keep an eye out for it. I wouldn't pay a premium for the 2.8/50 dL, ie any more than any other late 6 element lens like the EL-Nikkor, Rodogon or Componon-S, but if you get it for a price you're happy to pay then I'm sure you'll be happy with the results.
Here's an example of separation on a Computar dL 5.6/135 but separation can look like blotches anywhere around the rear elements (not to be confused with fungus which is common in enlarging lenses of all kinds).
Eggen, thanks for posting the link. This link, which is from within the link you posted,
http://photocornucopia.com/1072.html is about the 2.8/50 dL itself.