One other problem I faced recently was a very strange Segmantation fault in unit tests which was very difficult to trace.
The problem was fixed by upgrading to PHP 5.3.3.
Unfortunately Ubuntu guys are quite slow of updaing packages so to get PHP 5.3.3 under Ubuntu 10.04 LTS do:
add /etc/apt/sources.list.d/php533.list file with:
deb http://ppa.launchpad.net/nginx/php5/ubuntu lucid main deb-src http://ppa.launchpad.net/nginx/php5/ubuntu lucid main
apt-get update apt-get install php5
And you’re done!
If you want to fix apt-get warnings, you need to add they key specified on this page: http://launchpad.net/~nginx/+archive/php5 (look under Technical details about this PPA->the Signing key-what’s this)