I was just reading something, I found interesting, in another thread.
A few were commenting on the use of the phraseology:
I could care less; and
I couldn't care less.
It seems to me that use of both would be appropriate but are not equal or having the same meaning. It depends of course, to what extent does someone care.
Using the phrase "I could care less" would range anywhere from 1 - 9 on the "HP CARE LESS" scale (1 being the least amount of caring less). Using such a phrase means that you care less but could care less even more so.
Using the phrase "I couldn't care less" would be a 10 on the "HP CARE LESS" scale as, obviously, as so stated, the speaker could not care anymore less than they do. IMHO
It also seems, that depending on the extent someone cares, the phrase "I could care more" and "I could care less" may be the same, but not the same as "I couldn't care less", however, "I couldn't care more" can never be the same as "I could care less" or "I couldn't care less". The reason for this is simple. If one could care more, than obviously they care less, otherwise, they couldn't care any more.
At least, the user of any of the above identified phrases, cares. That is a good thing, more or less.