Hi Mary,
I respond depending on my mood. If I am very busy then I usually just look and don't respond. If I'm in a relaxed mood, then I respond on almost every picture I see. I also don't look at every picture posted. Sometimes I will only glance at 3 or 4 pics and then I don't come back on for several days and usually just look at the first page. I know that I miss a lot of pictures, but that is really all of the time I have to look on that day.
I learn a lot from every picture I see and I hope that you will continue to post your pics. Don't worry about the response, it just might be the time of day or that things are busy.