I'd heard the rumors about merging the two...
As I recall, when I tried to make questions in questionnaire optional, it still displayed them. I couldn't find a way to actually make them not show for the people who didn't need to answer them. And I couldn't get people to read directions and leave blank the ones that didn't apply to them.
Keep in mind, this was the 1.9 version...you probably made great strides after that. And maybe you could do that in old questionnaire but I couldn't figure it out. I'm not a techie person and only ended up doing what I do by accident (gremlins, to be precise--at least that's IT's story). In feedback, you can say this question should only display if that question was answered this way...so if someone said yes, I had technical difficulties, they could see a question that asked what were those difficulties? but the people who said no, I didn't have difficulties do not see the second question (if you set it up right).
One of the questionnaire things I loved that isn't possible in feedback is the ability to ask a series of rating questions in one question...you know, please rate the following on a scale of 1-5....I like cookies, I like cake, I like long walks in the rain...etc and have each option display in one question. In feedback, you have to build each one separate. .