I use my DF500 quite a bit, likely more than most, in a commercial cabinet shop. It has never gotten more than what you would call warm. It's really just warm enough that you could tell it had been running, if you just walked up and touched it. I use 6mm Dominos about 90% of the time and 8 x 50 the rest, so not a great load on the motor. I usually go through about 3 of the 1140 count boxes in a year, but I'm more than half way through the last bag of the second box and it's only mid June.
I have seen posts about heat from users of RO 150 too? I've never had a heat problem with any of my Festool gear.