Actually the biggest issue with the tilde key on the 660C/M is that you can't use ctrl+shift+esc to bring up task manager. This is because shift + esc = ~. I fixed this by creating an autohotkey script to bring up task manager when ctrl+shift+~ is pressed, but I guess it's too much of an annoyance for some.
Also I guess ` is a little inconvenient since it's fn + shift + esc.