Since I'm cutting foam, I'd be more concerned about the foam dust blocking up the optical sensors.

I'm not sure how aluminium swarf would impact magnets (sure, steel swarf would)...

I've got reed switches rather than hall effect devices (which can easily replace microswitches). However, I'm not sure about their accuracy for home switches. Since the frame of my machine is steel, I can easily move the limits since the magnets stick to it :)

(Seriously, I'd glue them down when I was satisfied they're in a good location).