Following the creation of a My Sites site collection I attempted to search for a user, but no results were returned.  I checked the search service crawl log and saw that the crawl of the My Sites site collection had failed due to “The item and all items under it will not be crawled because the owner has set the NoCrawl flag to prevent it from being searchable”.

In order to remove the NoCrawl flag, open the offending site as a site administrator.  Click on the URL in the error to open the site.  Open Site settings and navigate to the Search section.  Click on Search and offline availability.

Change Allow this site to appear in search results to Yes and save your changes.  Now re-crawl the site.