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Early on, I asked this question of support and was also told no, AdWord keywords and searches are not case sensitive.
I too have keyword lists where I careless pasted information in and ended up with the same terms in both lower and sentence case and receive separate stats and CTRs.
However, when I do an informal test, I see that my keyword is returned regardless of how I type the case and even in cases where I made a keyword upper case and searched lower case, my result was returned.
As far as the stats, my semi-educated guess would be that one of two things are happening:
1) When you repeat a keyword in your list with two separate case variations, the stats are kept based on how they were searched for by the user
2) The stats are kept based on which variant of the keyword the AdWords programs used to match the keyword with a user query.
Whether either of those answers are correct, by seeing that we have two separate CTRs for the same keyword, I would say it behooves us to stick to lower case since we run the risk of losing the benefit of an acceptable aggregate CTR when the keywords are being tallied separately like that.
We do not know what happens to "price" when "Price" has too low a CTR and becomes slowed or disabled. Will the other "price" remain viable? Why take that chance? For that matter, if "price" was borderline and "Price" had a 25% CTR with 4 impressions, wouldn't we want the "Price" to help "price" stay alive with that extra click?
Having worked with many programming languages over the years, it's always proven best to do all string comparisons by converting both strings being compared to lower case prior to evaluating. The only exception being if case really were important to the comparison, which it rarely is. In a Unix environment, one can have a file called FOO as well as a file called foo in the same location and they will be two separate entities. Is that desirable? Usually not.
It will be interesting to see if someone smarter than I can come in and answer this question authoritatively. That will also settle the issue of whether I am a FOOl or not :)