How to speed up the process of entering a group?
A speed killer is setting the variable gnus-fetch-old-headers to anything different from nil, so don't do this if speed is an issue. To speed up building of summary say
at the bottom of your ~/.gnus.el, this will make gnus byte-compile things like gnus-summary-line-format. then you could increase the value of gc-cons-threshold by saying something like
(setq gc-cons-threshold 3500000)
in ~/.emacs. If you don't care about width of CJK characters or use Gnus 5.10 or younger together with a recent GNU Emacs, you should say
(setq gnus-use-correct-string-widths nil)
in ~/.gnus.el (thanks to Jesper harder for the last two suggestions). Finally if you are still using 5.8.8 or 5.9 and experience speed problems with summary buffer generation, you definitely should update to 5.10 since there quite some work on improving it has been done.