Don't forget that just calling a function as &foo; without parens will behave like &foo(@_); by passing the current @_ argument array to the function. That can be a source of subtle bugs.

Personally, I always use parens on simple function calls. I may leave them out in method calls, but those are unambiguous anyway, both syntactically to the parser as well as visually to the programmer.

Makeshifts last the longest.