Agreed - lack of a Back button frustrates end users. This is made worse by the requirement that conditional logic start on a new page - once the user gets to the point where he sees the effect of his previous choices he can't go back and change them.
If it were an option rather than automatic, I'd be all for it. We all know circumstances under which we don't want them to be able to change previous responses based upon information to which they are exposed later in the survey.
As soon as possible, please! It would be great for the testing phase of assembling an online survey. And we should be able to include or not include the back button - it is appropriate only for some surveys.
I just joined last week and I've already got responses from users that they were annoyed by not being able to go back. As much as I like the tools provided by QuestionPro I may have to switch to other service if this problem is not solved.