Before switching to Canon Digital I was a Nikon enthusiast and built up quite a collection of those wonderful manual Ai-S lenses.
I used a Chinese made Nikon/EOS adapter with focus confirm on a Canon 400D.
The results were exceptionally good with fine vibrant colour rendition/no flaring on the following Ai-S lenses I tried: 50/1.8, 135/2.8. 200/4, 180/2.8ED.
A disappointment was the 85/2 (lack of contrast).
The surprisingly good Nikon lens was the lightweight non Ai-S 100/2.8E which gave exceptionally sharp images with fine colour rendition even though it had some fungi in it!
I even tried a friends Nikon 600/5.6 which also gave exceptionally sharp images unfortunately accompanied with a colour cast.
Manual focus on the Ai-S lenses is really nicely damped - much better feel than what you get with digital lenses.
Judging correct aperture/shutter speed comes easy after a few days - use PhotoShop for slight under/over exposures.
Lens jamming? Never had a problem!
And all the lenses reached infinity focus.
If you don't need AF and IS for a particular application then Nikon Ai-S lenses might be the way to go - they seem to last forever!