I agree that you are probably better off using HTML::Entities
The code you have should work for what you are trying to do.
The following snippet works as expected on your test line.

#!/usr/local/bin/perl -w
use strict;

my $line = q{<br>&lt;/pre&gt;<br>&lt;img src=http://blah.microsoft.com
+/analog_sc/bp/_lessons_learned/2788_1.jpg&gt;<br>&lt;br&gt;<br>&lt;im
+g};

print qq{LINE:[$line]\n};

tagremover( $line );

print qq{LINE:[$line]\n};

sub tagremover {
        $_[0] =~ s/&lt;/</g;
        $_[0] =~ s/&gt;/>/g;
}
[download]

Outputs:

LINE:[<br>&lt;/pre&gt;<br>&lt;img src=http://blah.microsoft.com/analog
+_sc/bp/_lessons_learned/2788_1.jpg&gt;<br>&lt;br&gt;<br>&lt;img]
LINE:[<br></pre><br><img src=http://blah.microsoft.com/analog_sc/bp/_l
+essons_learned/2788_1.jpg><br><br><br><img]
[download]

What are you getting in your $description var after the replacement? DOes your data have Newlines in it?

Wonko