RE: [h-e-w] how to close all buffers at once?

[Drew Adams]

Others have told you how to code this:
 (mapc 'kill-buffer (buffer-list))

It doesn't get any easier than that. But here's a twist, FYI -

If you happen to use Icicles, there are multi-command versions of many
common commands. For instance, `icicle-kill-buffer' is a multi-command
version of `kill-buffer'.

A multi-command acts just like a regular command (so it makes a good
replacement), but you can also use it with completion to act on any number
of things at once, selectively or indiscriminately - in this case, you can
kill one or more buffers with a single invocation.

You can use `C-mouse-2' to selectively pick them off in buffer
*Completions*, or `C-next' to mow them down one by one, or simply `C-!' to
kill them all.

The buffers you can do this to are those that match your current input; if
your input is empty, then all buffers match. You can use your input to first
filter the list of buffers you want to act on - use a regexp if you like. If
you first use `C-^' then you can include internal buffers (whose names start
with a space).

The same behavior holds for other multi-commands - visit buffers, files, or
bookmarks; delete files; toggle user options;...  whatever. Virtually any
function you can define to act on one foobar you can easily turn into a
multi-command to act on one or more foobars. Even if you never use the
multi-command aspect and always act on just a single foobar, it's good to
have around, it doesn't get in the way, and it's free.

http://www.emacswiki.org/cgi-bin/wiki/Icicles_-_Multi-Commands