这是好用的地穴吗？

I'm upgrading my auth class, replacing md5 with crypt for storing passwords. Here's the approach I've taken:

function crypt_pass($pass, $userID) {
    $salt = $userID .'usesomesillystringforsalt';  // min 22 alphanumerics, dynamic
    $method = (version_compare('5.3.7',PHP_VERSION,'>=')) ? '2y' : '2a'; // PHP 5.3.7 fixed stuff
    if (CRYPT_BLOWFISH == 1) {
        $blowfish_salt = '$'. $method .'$07$'. substr($salt, 0, CRYPT_SALT_LENGTH) .'$';
        return crypt($pass, $blowfish_salt);
    }
    return sha1($pass . $salt);        
}

Making the salt unique per user adds a step, a db lookup for the supplied username's id ... I figure it's worth it. Am I wrong about that? Is there anything else I'm not considering here?

The whole point of salting is to produce different encrypted strings from the same password. If you use the same salt every time, this will not happen, so you may as well not use salts at all. You should be creating a random new salt for every password, and then storing it in the database alongside the encrypted-and-salted string.