It kind of supersedes Windows Defender as well. I've been using MSE on several systems since it was released on Microsoft Connect, and it's been running very well, especially considering it is still in beta.
System Manufacturer/Model Number self built OS Windows 7 Professional 64-bit CPU Intel E8400 3GHz Motherboard Intel DX48BT2 Memory Kingston PC3-10700H 4Gb Graphics Card XFX Radeon HD 5850 BlackEd. Sound Card Asus Xonar DG Monitor(s) Displays 2x Samsung SM-T220HD 22" Screen Resolution 1680x1050 on two monitors
Keyboard Microsoft Comfort Curve USB Mouse Razer Diamondback 3G PSU Thermaltake ToughPower 850w Case Thermaltake Armor Cooling Scythe Mugen II Hard Drives OCZ Vertex 2 120gb 3.5" (OS)
Seagate Momentus XT 500gb
Samsung F3 1Tb (games)
2x Samsung F1 1Tb Internet Speed 8128/443