The original site and the best. Fifteen million searches performed!
About 36 million, including some duplicate email addresses.
You need to change all your passwords. You should use a unique, randomly-generated password on every website, and store them using a password manager like 1Password, LastPass or KeePass.
Ashley Madison did not validate account email addresses. It is quite possible someone else accidentally or deliberately registered using your email address rather than their own.
You'd be amazed how many people apparently don't know their own email addresses, so don't panic if you mysteriously find your email address on the list, especially if you have a common name.
You don't, but I'm the same person who made the Adobe leaked password checker in 2013 if that lends me any credibility.
Do not use the "Trustify" search site. They are recording email address searches and spamming/extorting people. More info