In IE6 and sometimes in IE7 the background images flicker if they’re also an <a>.  A small edition to .htaccess overrides the browsers default to load the backgrounds every time.

ExpiresActive On
ExpiresByType image/gif A2592000
ExpiresByType image/jpeg A2592000
ExpiresByType image/png A2592000

Reqires mod_expire on an Apache server (most have it).