I've no idea if their service actually works but if it does, it's illegal in the EU and it would also be illegal for their clients to use such information to e-mail those visitors.
EDIT: talking about relead.com mentioned in a g+ reply.
As an American who built several web businesses before moving to Germany 4 years ago, I now shudder at what can be legally done in the US. There is no real perspective of data privacy at all. Now, I often feel that the German (and proposed new EU) standard goes way too far. But, I'm a fan of at least something that can keep such creepy behavior away from identifying users until they identify themselves.
I realize I'm being idealistic in my stance, but I'm not a fan of going too far either. One thing I'm very happy to see in the EU is the focus on there being a standard. Today it it makes it difficult to manage a globally focused user base with so many different legal requirements. The proposed standard in the EU would make it easy to do business here and have a better framework for cooperation with the US than the safe harbor structure today.
Actually, it looks as if they stop short of personal identification, though they can achieve personal identification in some cases, depending on the size of the company, location of query vs location of key contacts, etc.
As I read their pitch, they identify the company a visitor to your site represents, and then they suggest the contacts at that company and give you a bunch of info about the company and the key staff.
EDIT: talking about relead.com mentioned in a g+ reply.