160: How do I make Gnus behave more like nn, where I scan all the messages
     and select the ones I want before I read any?

   Include this Lisp form in your .emacs file:

     (setq gnus-auto-select-first nil
        gnus-auto-select-next 'quietly)

  When you enter a group, mark the articles you don't want using `d' and
  `C-k', then expunge the ones so marked with `x'.  Move to the first
  article with `M-<', and start reading (with SPC).