seems a lot of people haven't heard of this, but it's a little gem! ... if you're comfortable using security programs in general you shouldn't have any issues with this. Its main purpose is to protect against software vulnerabilities that hackers exploit to create 0-day attacks, gain access to your system and so on. Especially useful for hardening your main vulnerability access points such as web browser, email client etc.
http://support.microsoft.com/kb/2458544
http://support.microsoft.com/kb/2458544
The Enhanced Mitigation Experience Toolkit (EMET) is a utility that helps prevent vulnerabilities in software from being successfully exploited. EMET achieves this by using security mitigation technologies. These technologies function as special protections and obstacles that an exploit author must defeat to exploit software vulnerabilities. These security mitigation technologies do not guarantee that vulnerabilities cannot be exploited. However, they work to make exploitation as difficult to perform as possible. In many instances, a fully-functional exploit that can bypass EMET may never be developed.