well i built that amp (**broken link removed**) but put a ne5532 in (only because that was what I had lying around). Its awful. I have only tested it with a pair of headphones plugged in, but it doesn't improve the volume a huge ammount, and there is masses of distortion and interference and everything that is bad about amplifiers is personified in what I've just built.
I suspect it may have something to do with the fact that I built it on a small piece of vero board (approx 35x15mm), and I have interference/crosstalk between channels, and perhaps interference from the power (although I am using a PP3 battery, so it should be fairly 'noise-free'). I have built small amps on vero board before, with no problems, so I'm a bit supprised by this.