It's there because in your OP you say "... I need to identify on what host each user-id ...". It's not used because I didn't need it to illustrate the main issue. However if you change the final print to:

for my $name (@unlike) {
    my @hosts = map {$entries{$name}{$_}{host}} keys %{$entries{$name}
+};
    print "$name found on \n\t", join ("\n\t", @hosts), "\n\n";
}
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then the output is:

bjose found on 
    /var/tmp/passwd.hostname2.platform
    /var/tmp/passwd.hostname1.platform
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I don't understand this logic or data structure, but I will attempt to explain it in English.

for every element in array unlike (which is username)
map keys values from hash entries to ??? with name and host.  Assign t
+his to the array hosts.
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I understand the print statement, but the data structure build I do not.

Why do you need keys %{$entries{$name} and why not just 
keys %{$entries}?
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I would like to see output like so or something to that effect:
I tried adding values uid and gecos but got errors and played for awhi
+le and could not get it printed correctly.
So you are using name and uid as the keys and host,gecos and gid as va
+lues?
I seem to struggle with hashes even though I have read Learning and Pr
+ogramming Perl. Any advice you have?
 
wlprdadm found with uids of 134 and 135 on
        /home/dbsmith/passwd.eipdbmp1.hpux $gecos
        /home/dbsmith/passwd.carappp1.hpux $gecos

as an example.

thank you!
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%entry is a HoHoH - Hash of Hash of Hash. The first hash is keyed by name. That accesses a hash keyed by UID. That accesses a hash keyed by various parameters including the host name. In the line:

my @hosts = map {$entries{$name}{$_}{host}} keys %{$entries{$name}};
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we generate a list of the hosts associated with a particular name. The hosts are in the 'host' parameter in the hash accessed by UID.

keys %{$entries{$name}} generates a list of UIDs for a given name. Remember that hashes and arrays only store scalar values so what is stored is really a reference to a hash. So the % sigil in %{...} dereferences the hash reference to be a hash which keys then returns the list of keys for.

For each UID in the list map {$entries{$name}{$_}{host}} retreives the host name - the map generates an output list with each element from the input list replaced by the matching host name.

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DWIM is Perl's answer to Gödel