Is it easy/possible to tell symfony2 to respect the "Accept-Encoding" header sent by web browsers and (if possible) gzip-compress rendered content in the response?
Based on http://developer.yahoo.com/performance/rules.html#gzip it seems like a good idea.
If you are using Apache httpd, then it is quite easy - Just enable the mod_deflate module in the httpd.conf and add AddOutputFilterByType lines for the different types (more info here: http://httpd.apache.org/docs/2.0/mod/mod_deflate.html). I do not believe that symfony2 can gzip something by itself, as this is normally a job for the web server.