The manual focus isn't a problem - I've seriously considered buying some of the Voighlander manual focus lenses - but the metering on the D80 will not work with an AIS lens so you'd have to do all the settings manually somehow or the other, either by trial and error, measuring with an external meter, using another lens or by the sunny16 rule. That's reduced amounts of fun if you're not doing tripod mounted still shots!

I think manual focus is great... And not so difficult on the D80 as you have the little green focusing dot (lower left in the viewfinder).

The main draw back might be the metering... The D200 allows for using the three metering modes with all old lenses in A and M modes... You can also memorize those lenses so as they show in the exif file.

I used them on my D70 but had to rely on the "sunny 16" technique or shoot , view, and shoot again after some aperture or speed modifications... Great for not fast moving subjects (meaning really slow :-) )

The manual focusing can be much more precise then AF, and the focusing ring has a much better feeling and has more "room" the the new AF ones!

"What can I do, What can I write, Against the fall of Night". A.E. Housman