Hi,
One thing I really like in Emacs is outline-minor-mode. A newbie question, 
though, can I easily interactively set the outline-regexp without having to 
evaluate Lisp code in a separate buffer, or update my config? My matching 
needs dynamically depend on the kind of content in the buffer, I use a 
regexp for matching functions when doing Lua, but would like to use a regexp 
matching numbered headings like 1.3. when viewing a text dump of the Lua 
reference manual.

In fact, I view outline minor mode as a kind of alternative UI to traversing 
regexp search results non-linearly. Which reminds me if I have n 
dot-separated sections e.g.
1.3.5
can I make outline-minor-mode understand the concept of subchapters and 
subsubchapters in its tree structures? I can regexp match the bits all 
right, though.

As to what's good in it:
Outline minor mode let's me easily hide function bodies and get the big 
picture, without having to use regexp matching to jump from function to 
function. It also makes rearranging stuff a breeze compared to selecting 
line by line and cutting and pasting, which is what I used to do. It also 
works great for languages not supported out of the box, such as Lua, if you 
just say something like:

(setq outline-regexp "function")

The Emacs wiki has taught me almost as many handy things as the book 
Learning Gnu Emacs, it is a great resource!

Further more, things are so much easier to manage from the keyboard if you 
go and redefine the branch management keys to emulate tree-control keyboard 
conventions. I found the following in the wiki and have it in my .emacs file 
(for Windows and Linux):

(global-set-key [M-left] 'hide-body)
(global-set-key [M-right] 'show-all)
(global-set-key [M-up] 'outline-previous-heading)
(global-set-key [M-down] 'outline-next-heading)
(global-set-key [C-M-left] 'hide-sublevels)
(global-set-key [C-M-right] 'show-children)
(global-set-key [C-M-up] 'outline-previous-visible-heading)
(global-set-key [C-M-down] 'outline-next-visible-heading)

-- 
With kind regards Veli-Pekka Tätilä
Accessibility, Apps and Coding plus Synths and Music:
http://vtatila.kapsi.fi