Are you certain they're not being given time in class for some of the work? I discovered with my oldest that she was using her in-class work time to chat and then was overwhelmed at home. You might verify first with the teacher that it is indeed all homework and not unfinished class work.
That being said, my kids routinely had an hour or two or homework. It didn't kill them, and they still had time to compete in sports, play with friends and enjoy veg time. My son, who started college this year, comments that he feels sorry for the kids who came from schools that didn't routinely give tough homework, because they were struggling to keep up the pace - whereas he found it no change over the work he'd done for the past 8 or 10 years.
I've found that my biggest challenge raising gifted kids is teaching them a good work ethic, The attitudes about not wanting to do work that is beneath them whether it was required or not was a huge issue in late elementary and mid school. And while I agree that homework can be mind-numbingly boring, it can teach discipline to suck it up and get through something that doesn't light our fire.
I know mine is likely not a popular opinion, but having hired high school and college interns in my company, I can tell you that a lot of these kids haven't had to do things they found boring. The few who were willing to do the demographic data research, compile XML from that boring data and do the other easy tasks I had - they were the ones who were given the fun assignments, because I knew they would pay just as much attention to the boring details as to the fun parts of the job. When we teach our kids to have a good attitude about their work, even when it's boring or pedantic, we help them acquire skills that will serve them well in adulthood.
