check this out. click http://2searchtech.com and your won't see a PR on your Google Toolbar but when you click http://www.2searchtech.com you see a PR4. Why is that?
because www is a subdomain of 2searchtech.com. They are two different sites and search enignes will recognize this as such. People fail to realize that www is a different site that just domain.com
Google treats the two URLs separately. I always make sure that any links on my sites and external link have the www in them so that I don't leak any PR.