Well Motortrend is a pretty darn good source. I drove one of my parents vehicles for several years after they had it details with the engine bay "steam cleaned". Never had any problem with it. I was thinking using a pressure washer in one of the bays of a do-it-yourself car wash might be risky too. I've never had a problem with any of my cars when I do that, and I've soaked some of them pretty darn good. It's just that this is a hybrid and it's engine bay is dirtier/dustier than any of my cars ever got.

* edit: Thanx for the tip about the CVTs Bob, the Civic Hybrid I'm looking at is a manual, but it's good to get that info out there for CVT owners, even if it's been said else where before.