The interface for Security Essentials is quite sparse and easy to get a handle on.
Any program that functions as an antivirus solution will have one of these: the scanning progress bar.
The other ubiquitous interface: updating. While the interface is trimmed down to merely a progress bar, additional feedback would have been useful as the update progress bar has a tendency to get to approximately 90 per cent complete and slow down. Knowing why this was happening would be nice.
The history tab maintains Security Essentials' simplicity.
The settings tab.
Sending information back to Microsoft is not an option with SpyNet, although one does have a choice to more or less information.
A nice touch is offline help. The default help goes to the online version.