Yesterday I found I had a conflict between mod_deflate and mod_fastcgi. The bug is known to Ubuntu, but the proposed fix has never been committed. So I tried to install it manually. Here are the steps:

1. Go to http://www.fastcgi.com/dist/ and get the latest snapshot (for me it was the 05-Oct-2009 snapshot)

   wget http://www.fastcgi.com/dist/mod_fastcgi-SNAP-0910052141.tar.gz

2. Extract and change directory:

   tar -xf mod_fastcgi-SNAP-0910052141.tar.gz 
   cd mod_fastcgi-SNAP-0910052141/

3. For Apache2, the installation instructions are in INSTALL.AP2. You just need to cp Makefile.AP2 Makefile and then make and make install. But make doesn't run and complains about a missing file instead

   Makefile:12: /usr/local/apache2/build/special.mk: No such file or directory
   make: *** No rule to make target `/usr/local/apache2/build/special.mk'.  Stop.

   Hopefully the fix is trivial: in fact apache2 is in /usr/share/ instead of /usr/local/, so the following command will fix it:

   sed 's/\/usr\/local\/apache2/\/usr\/share\/apache2/' Makefile

4. Now we can make and sudo make install. Don't forget to sudo apt-get remove libapache2-mod-fastcgi before. In my case I used checkinstall instead of make install to avoid messing the system.
5. Re-enable mod_fastcgi with a2enmod fastcgi.

That's it! Enjoy your browser not throbbing more than needed!