I just bought this today, and so far, have been impressed. I've been searching for some time to find a Spanish to English dictionary that was Kindle-compatible. All I had to do is change it in "settings" to my default dictionary, and PRESTO (poof!), all my unknown Spanish words were immediately visible just by a flick of the cursor. It is integrated and functions just as the default Kindle dictionary does. (It should be noted by newbie translation dictionary users however: The Spanish language has something like 14 verb tense conjugations, including the conditional, subjunctive, blah, blah, blah. When you are viewing a word in a different tense, you'll receive the "root" word and definition. It might be confusing to you, but persevere, it's how we learn). Overall, this was $6.39 well spent!!!
Just an FYI (on 1/22/11): I see comments and low-star ratings due to non-integration issues on the iPod, iPod Touch and iPad. This review was written in regard to it's integration with the Kindle. The real ACTUAL Kindle. It was written before the iPad even came into retail existence. Users of these other devices need to remember they are not using actual Kindles, but rather Kindle "applications" and should do a little research to see if certain features/options are available before buying. Hopefully, this helps with compatibility disappointments.