I was under the impression that you only have to worry about overscan if you, like me, purchase a rear-projection technology TV. LCDs and plasmas don't have that problem, do they?
It depends on the TV and the input you use.
My LCD tv, when I plugged a computer into its DVI video port, worked great and gave me 100 percent screen with 1:1 pixel ratio. But some other TVs assume that you're plugging a consumer DVD player into that port and give you a bit of overscan if you do.
Thus, the need to know ahead of time which behavior your TV is going to give you.
All non-digital inputs will definitely give you some overscan, no matter which TV it is.