I don't see much here that is specific to O/R mappers. What you seem to be saying is that when subclassing things you have to be careful not to conflict with methods in the base class. That's true of anything. If I subclass CGI.pm and want to add a method called param() to my class, it will conflict.
in reply to A Growing Dislike for SQL-OOP Mappers
As for add_to_*, well, you have to commit to some API sometime. I'm not really sure what you are complaining about there. When I don't like the Class::DBI methods, I make my own. If I stop using Class::DBI, I can implement whatever public methods I created using vanilla DBI or Rose::DB or whatever else I happen to switch to.