Yes! I am bothered when others say "The reason........... is because......" Using the words "reason" and "because" in this way would be repetitive.
INCORRECT: "The reason I ate all of the ice-cream was because I like sweet food."
CORRECT: "The reason I ate all of the ice-cream was that I like sweet food."
Oh, and improper use of pronouns bother the heck out of me:
INCORRECT: "If I was him, I would have finished my project days before."
CORRECT: "If I were he, I would....."
INCORRECT: "The dog runs faster than him."
CORRECT: "The dog runs faster than he." (Short for: "The dog runs faster than he does.")
Also, I completely despise it when someone uses a run-on. The most stupid, most common mistake (I think). Use the comma, period, semi-colon, colon, and transition words properly, like we learned in elementary school!
LEARN, people. :)
PS. I guess this is not ONE "mistake," but THREE. Oh well, they annoy me equally much.