I agree with Customic that this is actually best for people who are learning English, to have a way to instantly translate what they don't understand on English sites and have an instant rough approximation.
Imy: Have you used it? I learned Italian awhile ago, but I don't use it too often. Turning this on Italian is a good way for me to read more in Italian. I can see the errors within the text that is translated. Plus it's a fun exercise for me to see what they're saying in English, and then compare how I would translate it differently. I feel like this keeps my Italian from regressing or becoming stagnant. Is it perfect? Far from it, but it is another fun way to give myself more exposure to languages that I'm not actively studying. That being said, I recognize that this is not a good tool for beginners, who do not already understand the language, and may learn expressions that don't exist in their target language and be confused about foreign grammers, but for me, this is a good extra tool to continue learning vocabulary.
Also, I only recommend it on "fluent", where they translate the whole page. Just translated words here and there is lousy and no good for any learner, I agree.