IMO regardless of whether you use the plugin or plain DBI or whatever, you should wrap any database access calls in an eval{} (and RaiseError => 1 in dbh_config().) Too many different things can go wrong in a web app.

In what way would you like to handle the error that the DB is down?

As for the exception you're currently getting as a result, what DBI connect attributes have you configured?  The following snippet

            ...
            # use the parameters the user supplied 
            else {
                require DBI;
                $self->{__DBH}{$name} = DBI->connect(@{ $self->{__DBH_
+CONFIG}{$name} });   # DBH.pm:42
            }
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apparently raises an exception, so my suspicion would be that you've somehow set RaiseError => 1.

Maybe you could force a stack trace to get more detailed info on what exactly is triggering the connect, so you know what to put eval {} around?

Depends entirely on how your site is built (e.g. is it mod_perl or not), but I like to insert code that constructs the DB handle at a known point ... that is to say, not “lazily” ... specifically so that I can gracefully deal with the proverbial “ka-ka” when (not if) “it happens.”   If the operation fails, it will throw an exception which I can catch, so I can respond by throwing up a “this site is temporarily unavailable” message instead of ... well ... throwing up.   :-}

I put something like this in my instance script (and maybe in my application models, also):

use CGI::Carp  qw(fatalsToBrowser set_message);
BEGIN {
 set_message( sub {
   my $msg = shift;

   # message for development server
   #print "<h3>Server Error!</h3><pre>$msg</pre>";

   # message for production server
   print "<h3>Server Error!</h3><p>Please try again later</p>";

 });
}
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Then I wrap all my database stuff with eval:

  eval {
    $db1 = DBI->connect(
      $CFG{'DB_DSN'},
      $CFG{'DB_USER'},
      $CFG{'DB_PASS'},
      {RaiseError => 1, AutoCommit => 1, },
    );
  };

  if ($@) {
    die "Database error: failed to connect.\n";
  }
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This basically allows me to trap any DB related errors, and avoid sending too much information to the browser, unless I'm in "debug mode".