Different schools and different teachers set such variable amounts that it makes me wonder what evidence there is to suggest the value of homework. Our English primary got very shirty with dh when he said that ds shouldn't be punished (at aged 7) for not handing in all his homework (silly sod he forgot it was in his bag). He said if anyone should be punished it was the parents, as few seven year olds are self motivated to do homework without parental support (nagging, bullying etc). The teacher gave him a copy of the homework policy which stated that he purpose of homework was to get children ready for the workplace. At SEVEN! I thought this was absolutely ridiculous, apart from the fact that as working parents we do not have homework (at least not from work).
Learning spellings for weekly tests also seems to be a matter of debate - the US teachers thought it was a very odd idea, and the school had excellent literacy rates.
Reading I think is a good thing, but I preferred the approach of the US school, where they had boxes of real books all grade by the teacher, the child picks something they like the look of, and that's the reading book. They had a little log for home, with a couple of questions for the child to complete every night (like what is the main idea of the story, or what do you think will happen next), which the parent has to sign. Books from home were allowed too, so long as they weren't very different in reading level (ie no picture books for dd as she should be reading chapter books).
The only thing we liked about the US homework is that it was every night, so that you could work out a routine time for homework, and that it had to be given in every day so it couldn't be put off. I think it is useful for parents to know what their children are doing at school, but that the work should be set at a minimum level (say two topics, each with a single worksheet taking about half an hour). I can't see the point of stressing children and parents out when they should be spending enjoyable time together (I tell my staff that taking time off to recharge their batteries is more important than working late because they will be more productive the next day - I would have thought this applied to children too).