I have been wondering, for a while, why is it that I get errors about DEFLATE no being known.

  [Sun Apr 11 22:41:23 2010] [error] an unknown filter was not added: DEFLATE
  [Sun Apr 11 22:48:54 2010] [error] an unknown filter was not added: DEFLATE
  [Sun Apr 11 22:50:23 2010] [error] an unknown filter was not added: DEFLATE

I should have thought of it, the deflate module was not installed. That was it, but oh well... 8-)

To tweak your Apache setup, use the following two lines:

  sudo a2enmod deflate
  sudo /etc/init.d/apache2 force-reload

And you'll get rid of those errors.

Note: to my defense, I will say that the error message is a quite convoluted sentence... how do they know that it was not added if it is totally unknown?