I've noticed that metal doesn't seem the get anwhere near as hot on the
belt sander as the bench grinder. At least for the 4 belt sander that
I use the most. I haven't done a study or anything, but I think it gets
a lot more air flowing past the part I'm sanding, compared to the bench
grinder. The extra air flow lets me take off more metal with the part
staying cooler.

This is with a coarse belt (less that 120 grit) compaired to a standard
grey cutting wheel in a 6" bench grinder.

I have to agree that th belt sander is a more useful tool. If anyone is
going to get one, I'd suggest you get one where you can get your part
behind the platen to sand the inside of "U" shaped pieces.