just from a USER'S point of view:
I find search results pages in the index pretty unhelpful.
Unfortunately with google's love of big brands, I seem to get lots of them in the SERPs when I do a search for certain keywords.
What seems even worse to me is that it APPEARS like google might be indexing text content from adsense ads that appear on those search pages, too.
So I have seen results where the snippet in the SERP featured text from an adwords ad, or where I have gone to a page that was listed in the SERPs and found that the matching keyword ONLY appeared in an adwords ad.