.... switch to Gtk2 .... ;-) .... not that I have corresponding Gtk2 code for that, but at least the development is very active.....and bugs get fixed quick..... poor old Tk still does simple things well, but it's getting old and neglected

A Tk::Optionmenu isa Tk::Menubutton. You want to attach a balloon to a Tk::Menu here. You can access the menu associated with a Optionmenu-button using the menu() method:

#!/usr/local/bin/perl

use strict;
use warnings;
use Tk;
use Tk::Balloon;

my $mw = MainWindow->new();
$mw->title('Simple example');

my $status  = $mw->Label(
                  -width => 20,
                  -relief => 'groove',
              )->pack();

my $balloon = $mw->Balloon(-statusbar => $status);

my $menu    = $mw->Optionmenu(
                  -textvariable => \my $res,
                  -options      => [qw(A B C D)],
              )->pack();

$balloon->attach(
    $menu->menu, # pass the Tk::Menu instance
    -msg => [qw(a b c d)],

    #-msg => 'foo',
    # this works, but you get the same msg for all menu entries, of co
+urse
);

MainLoop;
[download]

works as expected on Linux. Windows is special in that events over Menu windows are not passed to Tk so Ballon will not work here. <Motion> bindings will not trigger here either...

And - yes: Balloon works with Listbox as well as with Canvas.

...works as expected on Linux.

Just tried it (because it looked like a good idea), but it doesn't seem to work for me, i.e. with $menu->menu I no longer get any tooltips at all, not even random junk ones. — Just for the record.  (Linux, Perl 5.8.8, Tk 804.027)