Just in case no one caught this, I will state it.
MW3's knifing got nerfed by the looks of the E3 demo.
If you watch it, not only does it look like it takes a bit longer to actually knife, but after that, it takes a long time for you to raise your gun again.
Besides if people complain about knifes- you must be ridiculously bad if you cannot shoot a guy before he comes that close to you.