Should i extend 3 yr warranty on dell 1720 laptop.. after feb 2011 when current one expires? What is cost?
If you want an extended warranty from Dell, or from any other supplier, you may get a more reliable answer by asking them rather than us. Whether the cost is justified or not is a personal decision that only you can make.

I always work on the principle that someone has to make money out of these warranties so the mathematical expectation is that it will cost you more than it saves you. I never take out any sort of extended warranty as I take the gamble that my equipment won't fail and can afford to repair it if it does. Whether this is a wise stance for you is not something that anyone else can answer.