There are very few sites this tool cannot be used on (such as those with flash registration forms, sites with multiple domains that use a different one for registration and login, etc.), but you can usually still change the password later and use it even in some cases. I would recommend this tool to anyone, simply because, being an IT guy, I know how foolish some people are with passwords. Using a hash function based on the domain prevents these users from actually using the same foolish password for every site, even if they use the same foolish password for every site. The only thing you really have to take into account is those sites that have restrictions on password length/characters. You have to adjust the password accordingly, but it's pretty simple. I give it a 9 out of 10.