I do, depending on cost of item, expected time before replacement, and cost of coverage.
I have a car that I never plan to get rid of, it gets extended always. I have in general recouped 80% of the cost of the warranties on it to date.
New TV, plan to keep it at least 5 years, extended warranty out to 5 years. While it is unlikely that the TV will fail, if it does fail I am out $1000 and if it does not fail, I am out the warranty cost of $125. So far, the warranty company has made money off me, but I have 4 more years to go... Spending 12.5% of the cost of an item to extend the warranty is worth it sometimes. Spending 50%, never.
Small purchases, less than $250 never get warranties, I can replace those items easily. Larger items that I would rather not live without for more than a short period of time, well, I want peace of mind more than a few less dollars spent.