Seriously people, learn the difference between peak, peek and pique. Nine times out of ten if someone says something like "oh, you've caught my interest with that subject," they will attempt to sound smart and end up saying "you've peaked my interest."
This is wrong, and here is why.

Definition of "peak" = the highest point in geometry.
Definition of "peek" = a quick look or glance.
Definition of "pique" = to excite or raise (curiosity or interest).

I just got through a heated debate with someone saying that there's many different definitions of the word "peak" and that "pique" is just another word that elitist Grammar Nazis added to a dictionary to feel important. This is incorrect. Why?

Saying someone has "peaked" your interest would be implying that they have made your interest in the subject the highest possible amount achievable. However, most people that say this phrase simply mean "Oh, you've caught my attention. Please continue, as I find this slightly interesting enough to listen to what you have to say, and possibly do more research at a later date." This phrase would be better filled with the word "pique" instead, and it means your interest in the subject has been increased.

Peaking one's interest would mean having the highest amount of interest obtainable in a certain subject. This would mean total and absolute obsession, as nothing else would be interesting in the slightest to you.
Peeking one's interest just doesn't make sense, since one can not see interest (unless you're looking at bank figures).
Piquing one's interest would make the most sense, as you're elevating curiosity levels in that subject.

So please, next time you feel inclined to use this phrase, use it correctly.