ACM Queue has an article entitled Syntactic Heroin which says that user-defined overloading (ad hoc polymorphism) is a drug.

User-defined overloading is a drug. At first, it gives you a quick, feel-good fix. No sense in cluttering up code with verbose and ugly function names such as IntAbs, FloatAbs, DoubleAbs, or ComplexAbs; just name them all Abs. Even better, use algebraic notation such as A+B, instead of ComplexSum(A,B). It certainly makes coding more compact. But a dangerous addiction soon sets in. Languages and programs that were already complex enough to stretch everyone's ability suddenly get much more complicated.

From ACM Queue - Syntactic Heroin
Referenced Fri Aug 05 2005 09:30:29 GMT-0700 (PDT)

This echoes comments that Damian Conway made last week at OSCON regarding Best Perl Practices. Students seem to be especially taken with overloading when they learn about it. Its a novelty to be able to define syntax looks like its a built-in. This article points out the dangers.