I don't have time to do all my homework. I have a really busy schedule. It's more a problem on the weekdays -- I get home at 7-7:30 every day.
I try to do all my homework though. I understand that it helps and I also understand that it is a price for compulsory education. Yet I also think that homework presents too rigid a learning approach. It forces you to read out of a certain textbook, do a certain set of excercises, and it often does not give you any "problems" -- only excercises.
Unfortunately, at the high school level, not everyone appreciates learning and is motivated to learn. Without homework, too many people wouldn't learn because they wouldn't be motivated to do so. I expect it improves in college, but I think that AP/BC/IB classes should have optional homework. (This means you can pick and choose which excercises and problems to do, based on what best befits your learning style.)
In the last two years, I did about 98% of my homework. This year's been hectic and different though, with personal issues, but it's all good now.