While painting dining room my wife noticed metal housing of dimmerswitch
Was hot to touch . Is this because switch has been on high setting all day?
It does not seem to getting any hotter it just stays hot to touch. Should we
Be concerned?

Maybe near max rating for that dimmer.
If you have a 600 watt dimmer and it is controlling 10 60 watt bulbs(600 watts) it will be warm. Mabe a larger wattage dimmer or lower wattage bulbs?