One of the major changes is in the Apache modules that work with authentication methods. If you have your own, or third party scripts that use Authentication, you would be well advised to read through the relevant Apache documentation, and determine if you should upgrade or install version 1.8.0 of XAMPP. Some Authentication methods may break.
Apache's Guide to upgrading to 2.4
A 'how I fixed tricky problem'.
http://systembash.com/content/apache-2- ... der-error/
Read down about Module Enhancements
http://httpd.apache.org/docs/2.4/new_fe ... tml#module
Some of the information may appear self-contradictory. (particularly about mod_access_compat) which apparently was a 'bridge' only for Apache 2.3)
http://httpd.apache.org/docs/current/mo ... ompat.html
The directives provided by mod_access_compat have been deprecated by the new authz refactoring. Please see mod_authz_host.
Many thanks to Altrea for his assistance on clarifying this.