This morning I was reading an article in a back issue of Harper's Magazine (August 2011 — I'm behind in my reading), and I could not quite believe my eyes when I read the following sentence:
The Patriot Act removed that wall, enhancing the FBI’s surveillance capabilities through new powers such as roving wiretaps, “sneak and peak” search warrants—which allow agents to search a suspected terrorist’s home without prior notice—and the expanded use of “national security letters,” which give agents access to personal records without requiring a court order.
Yes, it really did say "sneak and peak", and I expected better from Harper's. The archived version online has the error corrected, but I can't sneer about that, because I've gone back and fixed mistakes online before. Still, Harper's has professional copy editors who are supposed to make sure that sort of thing doesn't happen. (They're not alone: the Wall Street Journal has done it, too.)
You might guess based on their meanings that "peak" and "peek" have the same source, French "piquer", "to prick", which also gave us "pique", meaning that English has not two but three homonyms to confuse people. (And they do: Google "peak your curiosity" and prepare to be depressed.) A peak is something high and sharply pointed, and a peek is a quick, sharp glance, so they could easily have arisen from "pique". But not quite. "Peak", and its relative "pike", are from "piquer", but "peek" is an unknown quantity: all we know is that it's related to "peep".