E.Shupps summed up some My Site info quite nicely, and it is very handy given all the confusion around personal sites with what they are and how you can update them.
The MySite site definition (SPSMSITE) is intended to provide only the ‘Private’ and ‘Public’ page views for a user’s personal site; all other functionality (lists, doc libs, etc.) is handled by the Personal definition (SPSPERS). When customizing these definitions (if you want to provide MySite functionality, you have no choice but to customize the existing definition – I know it’s not supported but it’s there just isn’t any other way), it is important to remember that SPSMSITE is a full definition, with the same base set of included lists as all other defs.
While there are no direct links in the GUI for working with MySite lists, users can add list web parts from the tool pane and, by default, modify the list contents. Since MySite content is global (personal site content is localized to the individual user account), any changes to MySite lists will show up for all users; not an ideal situation.
To work around this issue, change the MySite permissions for Members and Contributors. Use the following URL syntax to access the MySite security page (there is no ‘Manage Security’ link for this area):
Check the Contributor and Member groups (and any others you wish to modify), click ‘Edit’, and uncheck the ‘Add Items’ right under the Select Rights section. This will prevent users from doing and end-run around list security by dropping list web parts onto the MySite pages and modifying the content.