I own a computer repair workshop and virus removals are a huge part of my business. Here are my observations:
1) There is no such thing as a free lunch. Free antivirus is OK, but it is always better to have a full blown security suite.
2) MSE is nice, and has a light footprint. But like every other antivirus package, it cannot and never will offer 100% protection.
3) Windows Firewall is in general easy to defeat, regardless of version.
4) There is nothing, ABSOLUTELY NOTHING, that will stop nasties 100%. There is always something one step ahead of the good guys.
5) Even the experts get viruses from time to time. Humans are easy to fool.
6) Smart people think about what they are clicking and steer clear of dodgy sites. If it seems too good to be true, it IS too good to be true.