Here are a number of papers and presentations that have been written about Horde and Horde components, listed roughly in reverse chronological order.
Universal Acceptance case study, as presented to the Domain Name Association.
Deployment and security of complex Open Source applications and Mobile Horde were presented at CeBIT 2012 by Gunnar in German. The presentations are available as a PDF and on Slideshare ("Deployment" and "Mobile").
Jan was interviewed by RadioTux at LinuxTag 2011. The interview in German about the freshly released Horde version 4 and the new development model is available on their website. An English transcript can be found on Jan's blog
Jan presented Application Building With Horde in July 2009 at the 1st PHP'n Rio conference in Rio de Janeiro, Brazil. This was an update of Chuck's earlier talks, integrating recent changes in Horde_Rdo.
In June 2009 Jan presented an Introduction to Horde Groupware at the fisl10 conference 2009 in Porto Alegre/RS, Brazil. Part of the talk was a live showcase but the slides introduce to a lot of advanced features of Horde Groupware.
Jan was interviewed by TechWorld Australia at the October 2008. The interview covering the current state and future directions of the Horde Project is available on their website.
Chuck presented Application Building With Horde at the March 2007 Boston PHP user group meeting. This talk covers what makes up a Horde Application, and building applications using RDO and Horde_Form.
Chuck presented Application Building With Horde at the January 2007 NYPHP user group meeting. This talk covers building Horde applications with more free-form interfaces and using new PHP 5 Horde components.
Chuck presented One-day Application Building With The Horde Framework at NYPHPCon 2006. This was a code-intensive tutorial, and is available as a downloadable archive with full source code and instructions.
SCOSUG hosted Chuck for an overview of the current state of Horde. The talk was well attended and included demos of subscribing to a calendar from Apple iCal, and syncing Palm Memos with the Horde Mnemo Notes application.
In February 2005 Jan did a talk about Developing a Horde Application at the 2005 Free and Open Source Software Developers' European Meeting by .
Applied OO PHP: APIs, Design Patterns and Useful Objects was presented at the 2002 International PHP Conference by Chuck Hagenbuch.
Jon was asked to write an article for Daemon News outling the implemention of IMP in a BSD environment. The article is available locally here . It appeared in the September 1999 issue of Daemon News (here).