I just upgraded from 5.1, and had a bit trouble figuring out what was
new.  Here is a list of what I found.  Maybe it should be added to the
distribution?

---- NEWS ----

* New features in Gnus:

** Support for trn-like graphical tree display.

Enable with (setq 'gnus-use-trees t).

** Topics.

Groups can now be organized into different topics.  Type `t' to
enable, and `T C-h' to get a list of commands. 

** Improve support for including old articles in thread display.  

The old code would only include articles that hadn't expired.  Enable
new code with (setq gnus-build-sparse-threads t).

** Allow composing multiple messages simultaneously.

You can now compose multiple news or mail replies simultaneously, and
you do no longer have to send the messages before you exit.  Enter the
`nndraft:drafts' group and type `S D c' to continue composing a message.

** Allow retrying posting a rejected news article.

If the server reject a news article, you can enter the
`nndraft:drafts' group and type `S D b' to try posting it again.

** Automatic logging of outgoing mail and news.

Disable with (setq gnus-message-archive-group nil).

** Support for off-line mail and news reading using the SOUP format.

Gnus will now create and read SOUP format packages.  Read the manual
before trying this! 

** New nn-like pick mode. 

This will allow you to pick the articles you want to read before
reading them.  Type `M-x gnus-pick-mode RET' to try it.

** New mode for browsing binary groups.

Type `M-x gnus-binary-mode RET' to try it.

** Restricted summary view.

The `/' key now allows you to restrict the summary view, for example
will `/ s gnu RET' restrict the view to all messages with `gnu' in its
subject. 

** The group buffer is now fontified.

See `gnus-group-highlight' for how to customize it.

** The group buffer can be sorted automatically.

Type `G S C-h' for a list of sort commands.

** Commands now work on the active region.

If the region is active, most commands will work on all items in the
region.  Use `C-u M-x transient-mark-mode RET' to enable active
regions.

** More flexible buffer configuration.

See `gnus-buffer-configurationų.

** Header buttons.

Mail addresses and message-ids in the header are now buttons.  Push
`mouse-2' or `RET' to activate them.

** You can now hide PGP signatures.

Type `W W p' to try this.

** NoCeM support.

You can now honor a secure replacement for cancels, somehow.

** You can resent messages with `S D r'.

** You can reparent mail messages with `T ^'.

** There is support for having multiple posting styles.  

So you e.g. can use different signatures in different groups.  See
section `Posting Styles' in the manual.

** Many bugs fixed and improvements of existing functionality.

** Even more new bugs.

** XEmacs specific enhancements:

*** Toolbar.

*** Picons support.