It's ok to do, just have to be careful where you direct the relatively high pressure. Yes electronics are "sealed" but that won't stop high pressure water passing through; even with good IP ratings. I've done a coil or two in my time.

Lol, so basically, don't wash spark ugs distributors and coils you should be fine. Obviously do t smash the pressure cleaner into a big wire conector.
I've wet a few cars at work. No biggie, compressed air and CRC.

In the 10+ years mines been in the family it's probably only been high pressure washed 2-3 times max!
Otherwise a damp rag and some tyre shine gets it looking mint!

If you don't let your engine bay get heaps dirty (I'm talking not being washed for 1+ years) you shouldn't actually have to high pressure hose it let alone touch it with a hose :S
If you wipe it down once every two months minimum it shouldn't even be too hard to clean...

That's my 2 cents anyway...

Rather the pull out the bucket and soap and sponge I'd rather pull out a can of degreaser and chuck a buck into the carwash, clean the engine, guards, subframe, everything in about 2 mins.