I dont think its worth the yearly fee, because its about to be canceled in june.
"Microsoft decided late last year to drop the Windows Live OneCare consumer security service in June 2009 and said it would be replaced by a free product, codenamed Morro, which remains under development."
I did the free 90 day trial after I had a problem I couldn't resolve with standard free devirusers and it worked but didn't want to pay for it. I shall wait I suppose...till...?