Some modules use hash keys beginning with a '-' for certain attributes of objects defined therein (witness, CGI.pm).

The use of a leading '+' before an expression within curly braces may be used to force Perl to treat the expression as a hash key or value, rather than parsing the whole thing as a block.

Not certain if this answers your question precisely, and I am particularly unsure exactly in what ways Perl 5.8 differs from 5.6, but this has been my experience with 5.6 and below.