I don't really think we should stress ourselves out on this challenge thing. First of all we should avoid using the word "rules" and as far as I am concerned this is just courtesy in that people should and try and comment on a few when possible.
Like Ann, I have time on my hands too, but it still takes an age to go through, so I am rather selective in how I comment. I don't think we should place a comment "just because it is in the challenge" and I'd rather be slightly more honest. If an image doesn't grab my attention for a comment, I won't place one. There will also be images I miss for other reasons.
It has been really noticeable how many colour images there have been in this challenge this month. And I don't mean "monochrome blue", but rather blue and green in one picture!
Someone remarked earlier "it is all too easy - all you have to do is convert to monochrome". I tend to disagree as you should choose a shot that will look good in mono. Maybe this is not possible every day, but think about what kind of shot works and what looks boring in mono.
Ironically, the proposed challenge for next month is based on comments, so I would expect more limited participation, in terms of people and frequency?
Happing snapping!
Ray