Same here... pressure washer is fine if you don't hold it an inch away from any of the engine bay components. Hold the end of the wand a "SAFE" distance away from most areas and you should be perfectly fine. Of course, one should exercise caution when cleaning an engine bay, i.e. cover any components that you think may pose a problem post-engine shampoo, such as air intakes, distributor caps, etc. Also, the method of engine cleaning depends on the condition of the vehicle. It probably isn't a good idea to start blasting water all over an engine bay that you know might have loose or frayed wiring (perhaps after a bothced repair job), whereas a brand new vehicle still under factory warranty would probably pose less risk. Remember, those who fail to plan, plan to fail. A neat trick is using compressed air to completely dry all of the nooks and crannies after the final rinse. Simple Green does a fine job of cleaning the engine bay however, I have heard complains from individuals that this can sometimes discolour certain metal components -be careful this doesn't happen. Another quick tip: before cleaning the engine bay be sure to rinse and wash the front fenders and any painted area near the engine bay area that you will be cleaning/degreasing. After rinsing the soap, re-apply soap with your wash mitt or favourite washing accessory (make sure it doesn't dry on the paint) this way if excess degreaser/cleaning product from the engine bay comes in contact with these painted surfaces, it will not remove any wax or protective barrier.
Finally, a nice application of Meguiars #40 vinyl and rubber cleaner/conditioner is a great way to accent a freshly-detailed engine bay. A word of caution: do not go CRAZY with this stuff and be sure to remove any excess product to prevent excessive dust build-up over time.
