I go into real time when I don't know someone. I continually and constantly evaluate what they say, what they do. *shrug* after all, I don't know them, and how will I ever if I don't pay attention to them; asking myself (and sometimes them) why they would say what they say, why would they do what they do? It may sound a bit cold expressed as such, but I'm really only doing what everyone either does, should do, or in some cases, studiously avoids doing.
It's helpful to remember that just because you evaluate a persons words and actions, it doesn't mean you have to negatively evaluate them, or if you see negatives, it doesn't mean you can't see the positives as well. Sure it gets tricky, but it's worth the effort. Afterall, doesn't everyone in a long term relationship at some point have to see the other person for who they really are, and accept the good and the bad? Why not sooner than later?
I think that there are actually several loose definitions of the phrase "benefit of the doubt" and people would do well to figure out just what they mean by it. Sometimes it's a nice, smart thing to do, and often it's just naive, selfish (as in not really about the other person anyway) and dumb.