The April 2008 issue of STC's Intercom magazine is packed with interesting articles about DITA. The contents can be found here:

http://www.stc.org/intercom/index.04.2008.asp

Whilst some of the articles are acccessible only by members, the STC have kindly made an article about DITA & Wikis freely available:

http://www.stc.org/intercom/PDFs/2008/200804_18-21.pdf