I get machines in day-after-day with MSE installed. The machines are constantly overrun with rogue antivirus and rootkit infections. The major problem with MSE is its absolutely horrible Heuristic scanning/zero-day detection. It has its benefits in being lightweight, integrating into Windows and being able to remove a lot of what it detects. It's detection rates however have been a glaring issue for some time.
I'm sure there's plenty of people who swear by it, because they've used it for a little while, and its prevented a few infections for them. Even the worst of antiviruses will have about a 50% detection rate. So that along with a little common sense, and MSE will likely work fine for you, but definitely no better than any other established AntiVirus. See review below.
The recent MRG-Effitas real-world scan did MSE a favor, by downloading the recently acquired infections and using IE to download them for the test. During this test, the antivirus being tested had 3 different chances to detect the infection... During the download, when download completed, and when opening the file. Again MSE failed horribly. This was a simple test, seeing how antivirus software performed when an infectious file was downloaded while browsing using internet explorer.
See report below.
MRG-Effitas Real-World AV Test - 1st-Quarter 2013