I have made this configuration a lot of times, but last week I had problem that I could solved thanks to this blog.
To configure People Search in SP2010, we all know that once you have your one Enterprise Search Site set up, you need to configure the scope and add the MySite url address to the crawling configuration. So go to CA –> General Application Settings –> Farm Search Administration –> Search Service Administration –> Content Sources and select your content source (normally Local Sharepoint sites). Here you need to add the MySite web application to the Start Addresses, but using the sps3 protocol, not the http.
I did realize that my User Profile application was running under HTTPS, but I thought that the sps3 protocol should work anyway. Well, that is NOT correct. If your User Profile web application uses HTTPS protocol, you need to add the sps3s to the Start Addresses configuration.
After that, check that the crawling account has access to the User Profile store checking the option in the Administrators configuration of the User Profile Service.
The People Search should work now.