The following line:

$main_new=$main->Button(-text=>"New",-command=>'newnote',
            -padx=>0,-pady=>0)->pack;
[download]

caused problems running this on a Win32 environment, but changing it to:

$main_new=$main->Button(-text=>"New",-command=>sub{newnote;},
            -padx=>0,-pady=>0)->pack;
[download]

ran perfectly.

Also, and this is just my own aesthetic preference, changing the geometry size of the notes to 100x100 makes them look a little more sticky-noteish, but that's just me.

xjar