A lot of people say “don’t use the dictionary at all when learning a language”. This is bollocks to the nth degree. For one thing, how are you supposed to find out what words actually mean?
The problem isn’t whether you use a dictionary, but how. If you use it for looking up words one by one as you attempt to write a document, then you’re going to be in a world of hurt. You’ll end up with things like “Apparence was given me that he had proceeded too great a distance”, rather than “It was obvious that he’d gone too far”…or worse.
As far as the learner of a language is concerned, the purpose of a dictionary is not merely to throw a word or two back in your face (that’s like giving a baby a firearm; it may end well, but more likely than not, there will be injuries), but to give you some direction as to how to use that word. The way it does that is through usage examples and any other guidance (like “this word is usually used in a negative form or followed by a negated verb”; “this word usually carries a bad connotation”, and so on). In the absence of a native speaker with oodles of time on her hands and an encyplopedic knowledge of her language, a good dictionary will take you far, far, far.
So, use a dictionary. But use it properly; use it to make progress; use it as a ladder and not a crutch — learn the example sentences in it (memorizing the meaning of the sentence and of the words it contains, such that when presented with the same example sentece again, you can correctly determine its meaning and pronunciation); that is, use the dictionary itself to break your dependence on dictionaries. After all, the more of the dictionary is in your head, the less you’ll need to refer to the dictionary. What will eventually happen is that you’ll be able to figure out the working of words just like you do in your native language — from context. In the past few months preceding this writing, I have finally reached this level in Japanese. Now I mostly look up new words out of curiosity rather than need; it’s become obvious to me what a new word means in a sentence, even without kanji. But it took a lot of dictionary-use to get to this stage. My dictionary became an extension of my skin, just as my headphones were of my ears. Now I leave the old Wordtank at home.
My 2 yen on that debate.