Actually, according to the American Heritage Dictionary, even in the present tense the correct word would be "used." For example: I am getting used to this new computer; or, I am not used to this cold weather. I am still not exactly sure how it came into use, but it appears to be from the Middle English. It is very odd, and I agree with everyone that says it just sounds wrong. However, having said that I will admit to using the term when I am too tired or lazy to form what may be a more grammatically correct sentence. (Similarly, I will end a sentence with a preposition when I don't feel like working at making a proper sentence.)