Hi Peter,
My Sites are hosted by a Web application and rely on a User Profile service application. Both are described in this section. We highly recommend that you
also have a Managed Metadata service application and a Search service application to use with My Sites, but neither is required. However, without these services, some My Sites functionality will be affected.
More information at Search service application
section in
http://technet.microsoft.com/en-us/library/cc262500(v=office.14).aspx#searchapp
Thanks,
Raghu