Obviously opinions will come into play here, and also it may depend on the particular brake system they're installed on. I put a set of these on one of my Bullits (Hayes Mags) mainly for the bling factor...coming from racing motorcycles, I thought all performance brake lines ought to be braided lines...and they pretty much are. Anyway, I didn't expect any noticeable braking power...I just knew they would be superior in durability. Well, I did feel the difference. I'm gonna go out on a limb here and suggest that perhaps some of you who have not noticed a slight braking power increase are running 8" rotors front and rear. I've long used an 8" on the front but was holding off on the rear...still using 6". I was getting to the point where I wasn't totally happy with the 6" rear on my Bullit as far as power. That extra length, extra fluid, and 6" rotor was just a little weak. The Goodridge lines allowed the 6" rear setup to be more than adequate...and this was because of less hose bulge for that long length of brake hose. My front 8" was already very strong...8" rotor and short brake hose is ideal anyway.
I think there is a discernable difference on many brake systems. They probably won't be as noticeable on an 8" front and rear rotor setups. Also they are more durable than plastic hoses for wear and for crashes. The downside...they are expensive.
On a side note, two other guys at the shop have also installed them on their bikes with similar results...and neither of these guys are "bling" oriented. One has Magura Louise FR hydros, and the other has those older XT twin piston calipers.