[FellsPoint]

When not in use, or just surfing the net, I put my clock speeds and memory speeds all the way down on my 4890. and it lowers my temps, i idle at 39c when they are all down. and when i want to play a game, i put them back to defaults and adjust the fan.

 

[Rewindlabs]

No of course not thats just fine...it may just be in vain as far as prolonging the cards life within the time you will actually be using it though but who knows (I do the same myself)

You can use an application to do that for you though

Rivatuner and Ati Tray Tools come to mind though and i recommend them both