I've been hit by panda 4 (40% decrease). I didn't see any change during panda 1-3. From what I've read it and when compared to my site, the change is probably due to the fact that I have over 30M pages indexed on Google, and they've starting seeing that as some sort of bad indication. Although I feel all of the pages have a unique value that Google should crawl, it seems I should make some tough calls and deduce the indexed pages according to some prioritization I will conduct. The question is what should be my target, or what factors should help me figure out a relevant target.
How many pages should I try to reduce to?
Is it enough to add
noindex to low priority pages or should I also remove all internal linking to them?
UPDATE: just to clarify, all of my pages are such that I believe will provide value to my users. But as I understood, in times like these I should still consider de-indexing some of them, because just because a user might get value, doesn't mean Google will see this as a quality page, which is a very subjective definition actually.