I've done it before, it seemed pretty safe, since almost everything is in some kind of sealed water proof container. I cover my alternator, battery, CAI, and any other electronics. Then I lightly sprayed down the engine and scrubbed what I could. I then dried as much as I could and let it air dry. You might have to eventually start the engine to evaporate the left over water, but their shouldn't be much left at this point. I would definitely suggest watching a few YouTube videos before attempting it, that should help you decide if you want to do it or have someone else do it.
It's all about the smiles per gallon