One other minor thing that you might think about is adding a little complication to the regex in your split in case the emoticon ends with a trailing "#". Of course this assumes the name cannot start with a "#".

while (<DATA>) {
    print join " <-> ", split /#####(?=[^#])/;
}
__DATA__
oX#####skullandbones
<;#####pie
(o)#####goatse
(~)#####ninja
:o)######clownwithbowtie

__OUTPUT__
oX <-> skullandbones
<; <-> pie
(o) <-> goatse
(~) <-> ninja
:o)# <-> clownwithbowtie
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flounder