There is new site that seems to get a lot of attention lately. It is called HackNotifier.
Basis premises are quite easy. You give them e-mail and they will check whether it appears in any of hacker released databases. For small sum of $5 per month they will check your account in real-time and notify you if it appears in fore-mentioned databases. For two bucks more it will even send you a SMS.
On their main page they claim total of 1,485,523 e-mail accounts that were hacked and invite you to check yours. In order to protect you they even have https certificate. But I keep on wondering how big an idiot you need to be in order to give them your e-mail...
Way I see it this is ideal e-mail gathering site. All that site operator needs to do is to save each e-mail that gets checked. After you get an e-mail, just increase counter on main page and tell user whatever. Most users either will not check or are not able to. Easiest way to collect accounts if you ask me...
Even if we assume that this site is legitimate (and that is huge stretch) what do you gain by checking your mail there or (in case of chronic stupidity) subscribing to their service. They let you know whether your e-mail is in some database. And what will you do with that information? Get new account? If you intend to do so, save yourself trouble and get new account each day. You will be safe.
P.S. Site can be found at www dot hacknotifier dot com. I do not want to link to them.