Microsoft have fixed Service Pack 1, resolving the issues with Search described here.
The Knowledge Base article includes the following:
The Search box is missing after installing the public update such as MS13-100 (KB 2850058). You may receive the “Sorry something went wrong” error message when you try to access the Search Center.
Service Pack 1 features bug fixes and introduces the ability to replace the SharePoint Newsfeed with Yammer.
Download Service Pack 1 from here: http://support.microsoft.com/kb/2880552