in reply to my $x or my ($x)
my $x and my($x) differ only when it's used on the left hand side of an assignment. In that case, when you write my $x = FOO, FOO is evaluated in scalar context, if you say my($x) = FOO, it's evaluated in list context, and the first value in the list is assigned to $x (undef if the list is empty).
A common example is a sub starting with sub { my($x) = @_; meaning that the sub would receive one argument and copy it to $x. In this case, sub { my $x = @_; wouldn't work, as it would store the number of arguments to $x.
This is, however, not specific to my: if you write an assignment like $x = FOO or ($x) = FOO, the same rules apply, only it doesn't create a new lexical variable $x but uses the existing variable.
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