"?"-placeholders are a lot cleaner, and use the same quote() internally.

$sth = $dbh->prepare('SOME QUERY WITH (' .
    $dbh->quote($foo) . ', ' .
    $dbh->quote($bar) .
    ')';
$sth->execute();

###

$sth = $dbh->prepare('SOME QUERY WITH (?, ?)');
$sth->execute($foo, $bar);

### And if you really, really want to quote() yourself,
## at least use join and map to make easy additions
# possible:

$sth = $dbh->prepare('SOME QUERY WITH (' .
    join(', ', map $dbh->quote($_),
        $username, $password, $email, $name, $url, $time
    ) . ');';

# But still, placeholders ARE better!
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++ vs lbh qrpbqrq guvf hfvat n ge va Crey :)
Nabgure bar vs lbh qvq fb jvgubhg ernqvat n znahny svefg.
-- vs lbh hfrq OFQ pnrfne ;)
    - Whreq