Chris, I replaced the 160 year old pine treads if my daughters This Old House with 5/4 oak. We were all real pleased with the results. As far as the "feel" of the stairs, I don't think anyone has had a problem. Of course, walking on their floors is kind of like walking on a ship anyway.
I had the specialty wood store joint the wide face and plane to a common thickness. I cut the boards longer than necessary with a panel cutting jig/sled (see Norm about this) and ran the "front" edges with a 3/4" roundover bit in a $60 Sears Craftsman router. Then I prefinished all the treads. For installation day, I removed a tread, measured the opening and checked it with a bevel gauge, then sawed them to fit tight. We could get under the stairs, and this helped a lot. You might knock a small hole it the plaster or drywall, just so you can see construction details and do this before you start in case there are any hidden surprises. The bottom tread was a woolybooger and I had to whittle with a cut-off disc on a Dremel tool because of a lot of trim, but other than than, no big problems. I just drilled smaller holes for and drove and sunk nails from the top, then filled the holes with the Minwax colored filler in the little jars. Drill and drive the nails at slight angles and they will hold the wood better.
Since we were there and the noise from the washer and dryer bothered people at night. I hung Homasote under the stringers and then put drywall over that. Cut the noise a LOT.
One interesting note is that the original wood for the house was sawed on a water powered up and down style saw mill that later became a flour and grist mill which has since been restored. More correctly, the beams from the shed and to support the saw works were used to build the grist mill structure. Henry in MI