My take - while you will see the occasional story of someone that was saved from a huge expense by an extended warranty, there are an untold number of people who threw their money away. The sales person will make you feel like your are a moron for not wanting to protect yourself 3-5 years out, while on the inside will see you as a moron for giving him $2-3K extra profit on his deal.
Bottom line - for every purchase where I declined an extended warranty, never regretted it. For every extended warranty I ever purchased, money thrown away.
I'll admit, the sales pressure is hard to resist, but do your best!
Edit - oh, look above... there's one now! :p