I bought 3 when they were $9 each. Don't intend to use them for nearly a year when the Trend Micro expires on our 3 PCs.
Why did I buy 3 and why so in advance? Yes, I know one copy covers 3 PCs. But unlike Norton, McAfee, Trend, et al, you aren't buying programs that get replaced every year. Buy Norton 2006 today for future use, and in 2008 you will be running software 3 years/versions old. With Live, you get the latest and greatest software when you install/activate it. Notice the packaging doesn't say "One Care 2006". So in 2007, 2008 and 2009, when I install the ones I bought in 2006 it should be just like the ones MS is "selling" then.
So I'm covered for all 3 PCs for 3 years with the latest programs as well as the latest definitions. Yeah, I know you can get the other big name AVs for free, but I don't need the hassles of 18 rebates (usually 2 per product, per PC per year) and often the rebates are one per household. I suspect the other brands will have to do the same thing before long, but even if they do, I'm still no worse off.