I've used various degreasers and pressure washer combos on more cars than I care to count (including quite a few 911's, there's not much in there to mess up). I've also done countless engines on stands and transmissions sitting on the ground out in my parking lot. DO NOT unplug the connectors, they're designed to keep water out. If you unplug them you'll be forcing a ton of water up into the part the factory tried very hard to keep dry.
Generally, I try to avoid spraying ignition components, open air filters, and computer stuff (air flow meters, ECU, ABS modules, etc...) directly. Otherwise, blast away. There's not really anything in the engine compartment that can't get wet, pop your hood one day after driving on the highway in a heavy rain and see if you can find a dry spot...