There was a movie made about homework a few years ago ("Race to Nowhere" was the appropriate title). I remember way way way too much homework - to the point where it was harmful as other posters noted. At some point the workload became so irrational that cheating was widespread as a coping mechanism.

We supplement school with projects at home - but the nice thing about that is we can turn the projects off if it stops being fun and constructive. It is a lot harder to stem the flood of school homework.