Superslow ist m.E. einer "normalen" Bewegungsgeschwindigkeit in keiner (!) Hinsicht überlegen. Im Gegenteil!
Im netz schwirrt sicher auch noch irgendwo das schöne statement von zyko zu diesem Thema herum (wo er sich auch auf Keough et al. bezieht).
Abgesehen davon fand ich folgenden Artikel immer ganz nett:

Is Superslow the Way to Go?

Recently, there has been a great deal of discussion about a style of training called "superslow". This is largely attributed to a recent article that appeared in a national magazine. The article interviewed various "fitness experts" who claimed that superslow was the safest and most effective way to train. The rest, as they say, is history.

According to superslow proponents, the biggest attribute of the technique is that it reduces momentum during training, thereby increasing force to the target muscle. In addition, by reducing momentum, the potential for injury is supposedly decreased. Sounds logical, right? Well, not exactly…

The effects of momentum on training are wildly overstated. Provided that weights are lifted in a controlled fashion, the target muscles are performing the majority of work and momentum is a non-factor. What's more, assuming proper technique is utilized, simply slowing down training speed will have no effect on reducing injuries. The science behind the superslow claims simply doesn't add up.

In reality, superslow training is actually suboptimal for achieving muscular development. You see, the weights used during superslow training must be extremely light to compensate for the slow speed of the lift. While this allows the concentric (i.e. positive) portion of the rep to be executed in the desired fashion, it takes away virtually any muscular stress on the eccentric (i.e. negative) portion. And since the eccentric component is arguably the most important aspect in promoting muscular development, results from superslow simply can't compare to performing reps at a traditional cadence.

What's more, superslow training is extremely tedious. The excruciatingly slow tempo causes most people to become bored with the routine in a relatively short period of time. This ultimately reduces exercise adherence - and if you don't train, you don't get results!

The bottom line with respect to rep speed is to follow the ABCs of lifting: always be in control. As long as you lift weights in a controlled fashion, the effects of momentum are negligible. Superslow is just another fad that will come and go; stick with the basics and you'll make optimal progress.
http://www.highnrg.com/newsletter/sep01.htm