No you don't have to use fully qualified object references throughout your code to avoid synonyms. Using stored code with definer's rights (the default) works, as does the ALTER SESSION SET CURRENT_SCHEMA command. There was a question about using that command in an AFTER LOGON trigger recently. Please see Avoiding public synonyms.

Just thought I would ask a question on this topic if you don't mind. If public synonyms are so bad then is the only option to have all tables/procedures/functions etc. prefixed by the schema throughout every bit of code? Does that lose a bit of flexibility or genericism of the code and application? Not sure if genericism is a word but you get the meaning right ;-)