I've been a professional Linux systems administrator since 1996. I started my career using Slackware 3.1 and RedHat 4.0. In the last 10 years I've used mostly Debian and Ubuntu on large, enterprise-grade servers in support of scientific computing.
I employ technologies like memcached, varnish, and APC to build responsive web applications, mostly in Drupal.
I use xhprof to examine and profile code and tools like Google Page Speed to ensure that I'm doing all I can do to accelerate content delivery.
I have been working intensively in using LDAP for a multi-disciplinary bioinformatics facility for the past 5 years. I had an interesting experience working with LDAP, PAM, and crypt.