Just as an example, MIT's electrical engineering graduate program doesn't require any GRE exam (subject or general). (Source: http://web.mit.edu/admissions/graduate/pdfs/MIT_department_info.pdf) I think graduate programs generally place more emphasis on research experience and undergraduate coursework than on standardized exams like the GRE.
I don't know, I think it might depend on the field you're in. If you're in physics, I imagine that the GRE subject test might carry some extra weight. However, if you're in engineering, since there is no subject test, the general test probably isn't worth that much. Either way, I imagine that research experience and recommendations count much more than GRE scores.
I'd say GPA matters a bit more. I graduated with a good GPA. While I also had great general GRE scores, my physics subject score was rather atrocious (about 45%-ile). Yet I recently got admission to an MS program. So I'm guessing that GPA is a bit more important than the GRE.
This isn't to say that the GRE isn't important. If you get low grades but do very well on the GRE, it can compensate for your GPA. Ohio State, for example, will consider applicants who fall below the 3.0 minimum, provided that they submit GRE subject scores. I have a friend who's got a 2.4 physics GPA, but who got a 75%-ile on his physics GRE, so such a thing is possible.
Anyway, I've got no expert knowledge on this subject; like you I'm just a grad school applicant. But this is what I've learned from my experiences thus far.
i think bad grades definitley will keep you OUT of grad school, but bad subject GRE's not necessarily. I think subject GRE's just make you easier to admit because it shows you have some physics skills (obviously you can debate how much but only an idiot would say there is no correlation between physics skills and subject gre scores). But the test is so weird that its common for smart people with plenty of physics knowledge to not do so hot. So a guy or girl with good grades and research and recs should be ok even with so-so scores but i would think that bad grades = trouble because if you can pull a 3.0 in undergrad physics how do you expect do in grad school when its required.