Yes, that aspect of operator overloading is nasty. I think one thing that makes operator overloading worse is that there are few reasons to use 'add()' rather than 'addUser()', but once you decide to use operator overloading, there are limited options.

C++ libraries which do abuse operator overloading (see the boost::spirit parser library as the best example) have this problem. For example, spirit wants to define the standard '' and '+' parsing operators. However 'a+' and 'a' aren't valid C++, while '+a' (unary +) and '*a' (dereference) are, so those are used.