A. I have never heard a CPU whine, and the G4s were hotter.
B. Specs. Any Intel machine will smoke any G4 machine at any task. Also, it's extraordinarily rare for any CPU to fail, so the G4 isn't any more reliable. The complaint about the GMA950 is legit, but the ATI 9700 isn't really relevant anymore either. As far as youtube goes, only the most powerful G4s can handle it anymore, and not HD content. The older machines can't offload onto the GPU for youtube anyway, so that's also a moot point.
A. All my intel toting Mac friend have a nasty whine with their machine, which G4 powerbook never has. Not to mention they always complain how very warm their machines gets(have to take their word for it), while mines doesn't. As for HD video I thought flash 10.2+ fixed that, as it allows the offloading to the gpu on most gpu, the 9x00 series included, with only the first gen i core and above supported, no?