Lovely surprise that came sometime after upgrading Lucid Lynx(and thus to PHP 5.3.2) – Xdebug doesn’t show local variables. Fortunately that’s a known issue that is fixed in Xdebug 2.1.0RC, but since it’s not released, it is not yet in Ubuntu’s repository. This should be pretty easy to fix though 
let’s try this:
sudo apt-get install php5-dev php-pear
That’ll get us ready for manual xdebug building. Then we need to get the sources. Gotta tell you, Xdebug guys are pretty awesome – they put together this nice little tool that helps you find and build the right version: http://xdebug.org/find-binary.php
It requires output of phpinfo() or in ‘php -i’ command and based on that gives you set by step instructions.
For standard Lucid Lynx install it boils down to the following commands:
wget http://xdebug.org/files/xdebug-2.1.0RC1.tgz
tar -xvzf xdebug-2.1.0RC1.tgz
cd xdebug-2.1.0RC1
phpize
./configure
make
sudo cp modules/xdebug.so /usr/lib/php5/20090626
sudo /etc/init.d/apache2 restart
Before restarting the server though(last command) you may want to double check the the following line exists in either /etc/php5/apache2/php.ini or in /etc/php5/apache2/conf.d/xdebug.ini
zend_extension = /usr/lib/php5/20090626/xdebug.so