(Note: this is a general answer to both Els's and WSC's comments.)
@Els: I think that this is a good idea to change the second answer into the one you suggested, so I went ahead and did so (it now reads: "I took the pictures between October 2011 and August 2012").
I also agree with your other suggestion (and I think it was also brought up by Jane, too) of adding the willingness-to-share option, so we now have 5 possible answers for Q9 (+ an "Other" option).
While preparing this survey, I've been reading some great survey tips from a Harvard University researched, David S. Walonick, who suggested that you should not present people with more than 5 choices for an answer, because it makes the survey/questionnaire too long and boring for the respondents, and I would like to stick to that suggestion. (It was also he who suggested to include a confidentiality/anonimity policy that I wrote down in the introduction.)
I am not sure how you know that "It was fun!" was a major motive that people chose in our previous survey(s), because I can't remember the 2011 survey results ever being published publicly (due to us not having the manpower to work on them). Perhaps you were talking about different surveys that I don't know about?
I am also not sure if asking people questions about placing the images on Wikipedia or using the Quality images process actually fits in the scope of this survey; this is a hard-core Wikipedian's job, and I doubt that the new users we try to reach with this survey even know how to place an image into an article, or what a Quality image is.
Question Y is included in our survey as Q15, and as for Question Z, I don't think that this survey is the right place to ask it. We might do so, but I would very, very much like us to limit ourselves to 20 questions; the survey cannot be too long, and it's already much longer than the one we used last year.
In any case, thanks a lot for your comments; I appreaciate them very much.