As somebody coming from the HCI side, rather than the software engineering / programming language side, I too value usability. But, it seems to me that you first do the major changes and then slowly hone to get usability right. I find lots of small little usability bugs in Pharo 3.0 but I assume that those are mainly due to the tools getting majorly upgraded right now. I'm not sure how to report these tiny usability bugs. If someone can chime in on the correct way to report these, I'd be willing to report them. For instance, I notice that when I am writing code in the browser and click to another method, I am no longer warned that my code will be lost. It is simply lost. That's a basic usability thing: Prevent costly errors. But, I assume that this is just a matter of Nautilus still getting refined. So, it may not even be worth mentioning.
My main contribution right now is being an early adopter of Athens and sending any weaknesses I find to the list. Athens is new and still has lots of little bugs. At the same time, it is ambitious and a major step forward for Pharo if it can be fully integrated. Of course, these little bugs will get taken care of as Athens is more widely used but part of the excitement of Pharo is that it is evolving. There are some areas where usability honing can be useful but others were the software engineering has to settle down before the honing can start.
Cheers,
Jeff