[kalleboo]

> It was always my assumption that grammar is the most important thing to learn about a language

I think it depends on what your goals are. If you just want to communicate, vocabulary is the most important thing to get started, since even with poor grammar people can infer what you mean (gestures help too!). I've seen too many people here in Japan who have crammed English grammar all their school years but are paralyzed when trying to communicate because they're just focused on getting the grammar right.

[iamnotlarry]

I think you should learn a handful of grammar rules right up front.

Obviously, * Desu/deshita/de arimasen/de arimasen deshita * Masu/masen/mashita/masen deshita

Then add a few more * if * while * want to <verb> * passive * honorific * etc.

You can learn one a week or one a month. There aren't very many to learn. But having just four or five up your sleeve (in addition to verb conjugation) can really improve your comfort.

[kalleboo]

Absolutely! You're not going to get anywhere in any language with only either grammar or vocabulary.