Allright, that first post of mine was the logic part of me speaking. Now for the personal side--
Homework with very, very, VERY rare exception is the biggest time sink that you can ever find. Homework is unrewarding and often times unhelpful, and it's not uncommon to have anywhere between 7-10 minutes, or more, of downtime in an hour long class. Teachers need to make use of this time to reduce the workload later. Sure, a half an hour of homework isn't bad, but a half hour from each class can easily come to 2 and a half hours or more of homework a night.
The solution to this problem? Well then, it's far easier to complain about a problem then fix it...
in response to BF--yes, learning's a chore. I'd love to spit out that proverbial quote of "You need to put something into it to get something out of this", but I think what's more fitting is that most of what happens in life is unpleasant, or dull, but there's no way around it. I'm not trying to support homework at all, and I know it's coming out this way. I'm just saying that, as inneffective as homework is, what's the alternative?