If you are interested in usability then UPA is worth a look. It is full of valuable information on why usability matters in software design and how to improve it.
The UPA supports those who promote and advance the development of usable products, reaching out to people who act as advocates for usability and the user experience. Members come from across the broad family of disciplines that create the user experience. We invite you to network in our community.
[from UPA’s web site]
There is a lot of information there. I’m still going though it myself.