As a result of our ongoing field research (AlejandroGoyenArielErlijman) we have found a series of XP implementation issues that repeateadly appear on discussion groups such as Wiki and EGroups (http://groups.yahoo.com/group/extremeprogramming).
Here are links to pages open for discussion. If you have any links/references to information related to each issue and/or its possible solutions, feel free to add them.
ExtremeProgrammingUnitTestCode: Should UnitTest source code be treated with the same importance as production code, or should it be treated as "second-class" code?