In previous versions of CiviCRM, a contact's activities were listed most recent first on the Activities tab of their record. This is handy for seeing what they've been up to recently.
In 4.7 they're shown oldest first. As we've been using CiviCRM since 2008 some of our data is OLD!
Is this a feature or a bug?
If it's a bug, it can be fixed by modifying line 42 of templates/CRM/Activity/Selector/Selector.tpl and changing "asc" to "desc".