The third (and probably the last) release candidate of PHP 5.3.0 has been published by the PHP Group a few days ago. Then I updated the preview packages for Debian GNU/Linux 5.0 “Lenny” on amd64 and i386.
To fetch them, just add these temporary entries in your /etc/apt/sources.list and upgrade your boxes :
deb http://php53.dotdeb.org stable all
deb-src http://php53.dotdeb.org stable all
Please note that an upgrade guide is being written. You also may want to visit this page.