To my ears, it's in the 5% improvement category....hardly earthshaking. It makes the top and mid a bit smoother, but you'll only really be aware of just what it's doing if you leave it on for several weeks, then switch it out. The sound is then slightly coarser by comparison. Weighed against that, you could argue that the sound has more life and presence without it (upsampling does seem to reduce dynamics). I do wonder what the effect will be when the DSPs can do 192kHz; it may be more worthwhile then, but at present it's marginal and programme dependent.

Cheers

George