+1 A great idea to avoid those spots that show up if you just let it air dry. There are lots of nooks and cranny's for water to sit in and catch more dirt.

 

Ive done it a few times on my Mustang and Focus at the local do it yourself car wash.
The Mustang I take a plastic grocery bag and cover the alternator and CAI filter.
Soak the warm engine in Simple Green, just a few min, i just kept spraying all over.
Then take the rinse mode and go to town (dont be stupid tho). Never had an issue on either car.
Also used the car brush a little on the underside of the hood and fender rails, radiator cover.

No pics of the Mustang, but heres a recent one of my beater focus that has 149,000 miles on it and never taken care of prior (my gf's old car)

 

There is nothing like a clean engine bay! That looks beautiful (well not as nice as the Mustang engine bay though LOL)

 

I have been using my leaf blower to dry the motorcycles and the engine bay. Look all over the engine compartment carefully beforehand to identify things you don't want to get too wet and then soak everything with Simple Green and spray off. I use the hot water from my sink in the garage for my power washer but most folks won't have that option. After it's all clean, blow dry and go for a drive.

 

Get the engine halfway to operating temp. park. vaccum out any loose debris. bag up (u may not have to but i do) the intake and alternator. get a garden hose sprayer with the shower setting. lightly do pulsed shots over the engine bay until wet. get simple green. spray that crap everywhere. close hood. wait 20-30 minutes so chemicals can bake. open hood. do more shower pulses to rinse. wipe dry. be happy