customize .htaccess and page optimization

I'm modifing my .htaccess to improve performance of my site and make page load faster.
According to this article and Yslow add-on I add header expired and Etag, now my htaccess looks like this:

RewriteEngine On
RewriteBase /

#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

RedirectMatch 301 /(.*)/\d{4}/\d{2}/\d{2}/(.*) /$1/$2

<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off

#Expire Header
<FilesMatch "\.(ico|jpg|jpeg|png|gif|js|css|swf)$">
ExpiresDefault "access plus 2 months"

FileETag none

the 301 redirection works,
but nothing change in my site and Yslow still continue detect the same error (header never expired and Etag). is this because I've a multisite installation?
(I'm have a wpmu upgraded to wp3.1.1 multisite with buddypress.)

Furthermore I installed the Wp htaccess Control plugin, and in the main site it say my current .htaccess is automatic generated by wp :

# BEGIN Wordpress

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END Wordpress

I'm intrested to create a Gzip compressio page too, I'm actually using wp cache to do it, but I guess configure .htaccess could it be better.