Lighting, Light Fixtures, Ceiling and Exhaust Fans - yard light dimmer

I recently installed a new yard light that has nine 60watt bulbs in it. The new 600w dimmer switch is getting warm, as noticed thru the wall cover. Just how safe is it to keep things that way?

This is from the Lutron website.

WHY DO DIMMERS GET WARM, AND IS THIS SAFE?
The technical explanation. During normal operation, solid-state dimmers generate heat. A solid-state dimmer is roughly 98% efficient-2% of the power is dissipates as heat, causing the dimmer to feel warm to the touch. The closer a dimmer is run to full output and the higher the load (watts) on the dimmer, the warmer it will feel.

This is perfectly normal and safe. Lutron dimmers are designed to the strictest UL safety standard, and can handle their full rated load (a 600 Watt dimmer can handle a full 600W of power*. Without overheating.

Although this is normal, as pcboss said, and you need do nothing, if the warm switch really bothers you, you can swap it out for a 1000-watt dimmer and it won't get as warm.