First impressions of Microsoft Security Essentials

I take issue with a company that creates an operating system, and then creates a security product to help keep said operating system safe.
The focus should be applied to fixing the operating system, not creating separate software to remedy the situation.

I am of course speaking about Microsoft, their Windows operating systems and their Live OneCare suite of security products which you had to pay for! That's right, you pay for an insecure operating system and then you have to pay the same company more money to help you protect it.

Microsoft's Anti-Virus, Anti-Spam and Anti-Malware changed its name for the PC version to Microsoft Security Essentials; and thankfully – it's now free. (That's a point for you Microsoft, but it should have been free in the first place.)
However, since hearing about the new and free version I must say all the comments have been positive.  From all reports it has been successful in detecting threats and cleaning them.  Quick to remain updated and importantly for this category of product; it has a small footprint on system resources.
So I have been looking forward to putting it through its paces – and today I found a perfect candidate.
I received a call from a small family business today asking me if I could help with one of their PCs.  They said that they had received a warning from within their browser (Internet Explorer) that their computer was at risk and they needed to download a certain anti-virus application.
Blindly following these prompts, they installed this anti-virus software and to their horror discovered that instead of protecting their computer that had infected it.

The warning they received was a fake; a clever and deceitful way for bad individuals to infect your computer.  (See 5 ways to secure yourself online post for more info).

I securely accessed their computer remotely (as my Citrix GoToAssist Express software allows) to find many pop-ups, warnings, and errors cluttering the screen.  These days it's hard to tell which are legitimate and which are not.
I thought to myself that I would need a miracle to save this machine.  I then remembered Microsoft's latest offering and decided “If Security Essentials can fix this computer than maybe it is as good as everyone says”.
I began the download process (which was quick) and then the install process (which was also quick).
In no time the software was ready to scan the computer.  I decided to initially perform a quick scan.
It immediately picked up 7 threats.  The computer was infected with trojans, worms and viruses.  The unholy trinity.
Within 10 minutes the quick scan was complete and I told it to perform the tasks of cleaning up the system.
Usually with these viruses etc, you can't clean them off straight away.  You have to restart the computer in safe mode or boot from a CD or some other time consuming activity.
So I wasn't too excited when Security Essentials told me it required a reboot to finish the process off.  I thought to myself “Yeah sure it will be all clean after I reboot”. 
Not to my surprise, when I restarted the computer and started another quick scan, the same 7 threats were there.
However, when I told it to clean this time…it did it.  It was clean!  The 7 threats were gone!  No safe mode. No boot from CD.
I was shocked, and very impressed.
A free anti-virus, anti-malware product that cleaned the PC – with only 1 reboot.
Maybe Microsoft know how to write a good anti-virus product – well they should.  It is their own system they are protecting.  Maybe that's why it has been getting positive reviews.
What have your experiences been with Microsoft Security Essentials?