Well, one thing I've noticed with the Wordtank is that it has several dictionaries including Japanese-Japanese (it uses Daijirin), English-Japanese, Japanese-English, English-English, English-Chinese, Chinese-English and a few others. My first thought was "why would I ever need that many dictionaries?!" Originally I didn't think I'd use or need even more than a couple of those, but I've found it's more useful than I thought it would be.
An example was when I was reading the manual for the Wordtank and it said something about having the ability to look up idioms and I was like "idiom... man, I feel dumb, cuz I'm pretty sure I know this word, but...." so I hit the Eng-Eng dictionary to look up idiom:
idiom - group of words whose meaning is different from the meanings of the individual words. Ex. 'Let the cat out of the bag' -> tell a secret by mistake.
Oh right... idiom... duh. Then say you wonder how to say one of the words from that example in Japanese, let's say 'secret'. You highlight 'secret' and tap it and it pops up a list of any entries in any of the dictionaries that have the word 'secret'. I see it's in the Eng-Jap dictionary and tap on that entry to go there. The Eng-Jap entry for 'secret' shows what the Japanese word for secret is and happens to be 2 kanji... but no kana or anything that shows you how you'd pronounce it. If you're not familiar with those 2 kanji you can highlight them and tap them and it shows you any dictionary that has those 2 kanji together. So you highlight the 2 kanji and tap them and up pops all the dictionaries again and I see that the Jap-Jap dictionary is the 1st result and tap on that and it brings me to the Japanese definition for 'secret' and the very first thing it has is the kana pronunciation for these 2 kanji together -> 'himitsu'.
So I've noticed that when you have all these dictionaries tied together like this that it promotes jumping around a lot more and you seem to be able to do a lot as a result and also learn a lot.
I've also had a few times where I highlight some Japanese, usually kanji, and tap it cuz I have no idea what it's saying, try to look it up in the Jap-Jap dictionary but there's too many words I don't know, and then don't see any entries in the Jap-Eng dictionary. *BUT* I'll see a result in the Chn-Eng dictionary and tap on that and now I see a bunch of English words that help me to figure out the meaning. I never thought the Chinese dictionaries would be useful at all unless I started learning Chinese, but I've actually run across this a few times.
I've heard Daijirin offers an Eng-Jap dictionary but not Jap-Eng. I'm not sure about Daijisen. So I'm curious if anyone has done anything like what I'm talking about above with the iPhone with either of those iPhone apps and just how much of this scenario could be done w/ either of those programs, if at all. I'm mostly interested in just using one of those 2 apps without having to bounce in and out of different apps, but I guess I'd be interested to hear anyone else's experience doing the multitasking thing as well and how easy (or painful

) that is. I've tried to find more English reviews of both of these iPhone apps and none really give the depth I'm looking for, so I thought I'd throw it out some line on some forums myself.