The documentation (https://docs.alfresco.com/6.1/concepts/sf-ref-template-guidance.html) contains details on which placeholders are actually supported in Smart Folder queries. In essence you'd need to replace %MY_PERSONAL_FOLDER% with %CURRENT_USER%. The PATH field allows for queries against the qname path of a node. As such, it must reflect the qname path of the search context, not the display path. E.g. PATH:'/app:company_home/User Homes//*' actually contains mixed elements - "app:company_home" is a qname path element, while "User Homes" is a display path. You can check the qname path by using the Node Browser admin tool to browse Alfresco's data structures, which lists the "path" for each node at the top of the details.
Querying for content in user homes e.g. requires the query PATH:'/app:company_home/app:user_homes//*' and excluding contents of any users home requires PATH:'/app:company_home/app:user_homes/cm:userName//*'. It is important to note that the local names in qname path elements must be properly encoded according to the XPath specification, so e.g. a user name of "User 123" will result in a home folder qname path element of "cm:User_x0020_123" as the white space must be encoded. For that reason, it may be problematic to use the %CURRENT_USER% placeholder to construct the PATH query, unless it can be guaranteed that no user name will ever contain a character that needs to be encoded (i.e. non-ASCII / non-alphanumerical characters, leading digits).