Isleaked is weird in that it was registered before the leaks were public... But I don't know what harm it's going to do other than take your email address and mark it as special or something. The list of emails is already out, so at this point, there's nothing you can do to prevent someone from trying what is listed in the file.
Keep in mind, these passwords aren't from Google or any of the other sites. They're from logins used to access other sites, meaning that if you are
BobSmith@gmail.com and you sign up to TheBestSiteEver.com with the username (or have as an email contact)
BobSmith@gmail.com, and you use Password123 as your password, these credentials will be stored on TheBestSiteEver.com. If someone hacks TheBestSiteEver.com and gets the database containing usernames/passwords/emails, they can create these lists. You're ONLY screwed if you use Password123 as your password on sites other than TheBestSiteEver.com, as this is where the email/password association was created.
I've since found the password list and verified what was in the list as my password. I've *never* used that password for anything important; especially not an email account. I did find passwords for a few friends, one of which was quite shocked that I knew that password.
To Estor and anyone else with a password creation/retention issue, try
LastPass or a similar service. Everything is encrypted client-side, so even if LastPass were to get hacked, someone would only get a blob of junk for your account. They'd also have to figure out who the blob belongs to... So it's unlikely that, if you had a sufficiently complex password, anyone could get into your account. You can also enable two-factor authentication on LastPass, so you're doubly protected.