As anyone could have guessed it earlier, Windows 8 promises to include Microsoft Security Essentials out of the box. This is a major step forward in the right direction for Microsoft because Windows is still the most popular target for viruses. This move certainly will help curb most malicious codes from infecting Joe's PC.
Also, it raises the bar for other AV vendors. The question is can your products beat something free, something usable, something common, something built-in, and enabled by default? I reckon some AV vendors will have to move up the ladder and leave this ground to Microsoft. Maybe they'll shift their focus on "managing"/cooperating with Security Essentials instead of competing with it.
We shall see.