Service Pack 1 for SharePoint was released a couple of weeks. Unfortunately it appears to break Search in SharePoint Foundation and it doesn’t look like we will see a fix until the April 2014 Cumulative Update is released at the earliest.
More Details can be found in this article “SharePoint Foundation 2013 broken search experience”
I have seen this problem first hand on two SharePoint Foundation sites. Others are reporting that the problem occurs after installing KB2850058.
The bad news is that this update cannot be rolled back. Once installed your choices are put up with broken search or install a new SharePoint Foundation farm.
UPDATE: 24 March 2014
Microsoft have released a fix to resolve the issue: http://support.microsoft.com/kb/2760625