Some people prefer to construct their objects using blessed array references. They feel it makes the object a little more opaque - unlike hash keys there is nothing in an array to indicate which variable has which meaning, thus making it harder to bypass accessor methods to get at data.

I have never heard this rationale before, but it smells of "Security through obscurity" rather then any real solid reasoning. The most widely used array-based OOP module I know of is POE and that choice was made very specifically because of performance. Of course this was like 1999 performance, so how applicable that still is on modern systems I don't know.