I kinda wonder if Korean and Japanese are related in some way, because the grammar is really similar (but the vocabulary is largely different, although there are minor similarities, much of it is because they were a former Japanese colony).
Looking a bit at Korean, and knowing some Japanese, if I had to make a semi-educated guess, they were related in the distant past (maybe 3,000 years ago).
Reason I suspect this (and some others do as well) is they share grammatical features amongst themselves that aren't found in any other languages.
@calvin The Altaic hypothesis... I can only charitably call it extremely tenuous at best... and my personal opinion is it's all a load of bunk.
@calvin The Altaic hypothesis is up there with Proto-World; there might be a modicum of truth there, but it's unlikely there's anything deeper than superficial similarities.