Microsoft Free Antivirus

The history of Microsoft with antivirus is not great but they are now providing Microsoft Security Essentials http://www.microsoft.com/security_essentials/?mkt=en-us for free (they couldn't sell onecare cos no-one was buying). I'm guessing it will be quite cute and cuddly but will possibly not be that good on what it's meant for (detection or removal of viruses), will be 100x larger than it needs to be and may contain lots of bugs - in common with other MS softs, I am told.