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
System Manufacturer/Model Number Samsung NP530U4B-S02IN OS Windows® 8 Pro (64-bit) CPU Intel® Core™ i5 Processor 2467M (1.60GHz, 3MB L3 Cache) Motherboard Samsung Electronics Memory 6GB DDR3 System Memory at 1,333MHz (on BD 4GB + 2GB x 1) Graphics Card AMD Radeon™ HD7550M 1GB DDR3 (Ext. Graphic) Sound Card Realtek High Definition Audio Monitor(s) Displays 35.56cm (14.0) SuperBright 300nit HD LED Display Screen Resolution 1366x768
Hard Drives 1TB S-ATA II Hard Drive (5400RPM) with ExpressCache 16GB SSD Internet Speed sucks Antivirus Microsoft Security Essentials Browser Google Chrome (Sync enabled)