i could care less

<<"I could care less" is simply sarcasm. We do indulge from time to time, you know. We have lots of phrases that are seemingly contradictory, yet make sense when you realize that they are meant to be ironic. The classic "You don't say?" is one. So is the exclamation, "NO, she didn't!"
>>

Fascinating. I never thought of it that way. Thanks Uriel! The phrase actually does have merit then! ; ]

With the other examples, "You don't say?", "NO, she didn't!" --it's easy to detect the sarcasm by the speaker's tone. But I fail to hear it in "I could care less" (which might actually add to the sarcastic effect...), but anyway... Great input.

"I could care less" is a wonderfully sarcastic Americanism with its roots in New York Yiddish culture.

Anyone who would want to see it neutered and stripped of its character by inserting a negative is a boring pedant and an enemy of real, living English.

<<With the other examples, "You don't say?", "NO, she didn't!" --it's easy to detect the sarcasm by the speaker's tone. But I fail to hear it in "I could care less">>

You're right -- instead of a heavily sarcastic tone, most people throw out an "I could care less" with an offhand flippancy that is even more disdainful and dismissive. The intention is not to mock so much as it is to convey that it isn't worth their time or effort. It's coolly contemptuous. That attitude is part of the intended effect. ;)