If you don’t like to get an access denied error message when you crawl the user profile at root sps3://sp2010 or you hate to search people and find 0 results, you have to grant to the Default Content Access Account permissions to the User Profile Service Application.
Go to the Service Applications page, click on User Profile Service Application (highlight it, don’t click on the link). When its highlighted, click on the Administrators button at the top. This gives you a window that looks like this.
If your crawl account is not listed, add it and then select the checkbox Retrieve People Data for Search Crawlers.
Once it’s done, you need to do a full crawl.