The main thing that bugs me is that, although it has an option to go through and highlight displayed English words on the screen (when an example sentence or phrase is given, allowing you to quickly search the definition of that English word), it doesn't give you that option for Japanese. So if I see an example sentence, and there's a word in Japanese that I don't know, I have to write it on the screen with the stylus rather that highlight it somehow. This can be a little annoying for kanji especially as I might not know the correct stroke order, thus making it a little tedious. (In actual fact, it might very well have this option, maybe I haven't found it yet???)
My Canon electronic dictionary, however, allows me to go through the displayed words and highlight anything, Japanese or English, and have the definition brought up immedietely.
Another thing that my Canon can do that the DS can't is give me an animated diagram of stroke order.