school homework unnecessary?

I've seen a few articles over the past few years questioning the value of homework in schools (I'll admit I think we demand a lot of kids, with several hours in school, and then perhaps a few more hours doing homework; I, for one, don't work that many hours now). I don't know enough about studies, statistics, or a gazillion other things to know if this is either reliable or valid...  but I was intrigued by this article suggesting there's only a limited correlation (and no cause) between homework and either test scores or grades.

From the linked article:

Was there a correlation between the amount of homework that high school students reported doing and their scores on standardized math and science tests?  Yes, and it was statistically significant but “very modest”:  Even assuming the existence of a causal relationship, which is by no means clear, one or two hours’ worth of homework every day buys you two or three points on a test.  Is that really worth the frustration, exhaustion, family conflict, loss of time for other activities, and potential diminution of interest in learning?  And how meaningful a measure were those tests in the first place, since, as the authors concede, they’re timed measures of mostly mechanical skills?  (Thus, a headline that reads “Study finds homework boosts achievement” can be translated as “A relentless regimen of after-school drill-and-skill can raise scores a wee bit on tests of rote learning.”)

Hrmph.