I just had a back and forth comment conversation about adapting Nikon Manual lenses, and here's a video from Caleb Pike of DSLRVIDEOSHOOTER.com that might help break down some of those questions. As far as adapting random lenses to smaller sensor cameras, Nikon's manual aperture ring makes them one of the favorites. The fact that you can still buy some of these Nikon AIS lenses 'new' as opposed to taking chances on 50 year old lenses is another plus. [Thanks Caleb].
It doesn't stop there. These Nikon lenses of course can also be used on Canon DSLRs without a large adapter, just a very thin shim-like adapter (check out Nikon to Canon EOS adapters). Caleb mentions a few great places you can grab these Nikon lenses, but you can also find some 'new' and 'used' lenses at B&H Photo Video. (Click here to find New and Used Nikon Manual Aperture Lenses).