What do you think about Microsoft Security Essentials?

Have downloaded and so far all good. It poped up a box just seconds ago asking if I would like to send dropbox.exe to Microsoft for a analyse. I cancelled it because I Love Dropbox.

What is your thoughts about this antivirus program from Microsoft?

Microsoft Security Essentials works well on VISTA and Windows 7. It is not our favorite security system, but it is pretty good for a Microsoft product... better than McAfee or Symantec - Norton, or Computer Associates or Panda.
Also, the reviews we have seen have been very positive.
We do not like to give high marks to any new security package... It deserves the test of time and scrutiny from a large number of users.

Then my question is, which is your favorite (free) security system?

No one product does it all.
We have 300 home clients on Avira Antivir, SuperAntiSpyware, MalwareBytes, and Windows Defender.
We have minimal problems on these homes where usage runs all over the map...

Alternates we like are Avast, SpySweeper, Spyware Doctor, and AVG 9.0 with reservations.