If you happen to develop PHP applications in ~/pubic_html instead of in /var/www and you have just upgraded to Ubuntu 10.04 (Lucid Lynx), you will be surprised that your PHP applications are not working anymore and your browser just prompts you to download something.
It turns out that the following lines were added to /etc/apache2/mods-enabled/php5.conf.
# To re-enable php in user directories comment the following lines # (from <IfModule ...> to </IfModule>.) Do NOT set it to On as it # prevents .htaccess files from disabling it. <IfModule mod_userdir.c> <Directory /home/*/public_html> php_admin_value engine Off </Directory> </IfModule>
Follow the instructions in the comments and restart Apache. Your PHP applications will be back to normal again.