When two parts are press fit together (e.g., headset cup and head tube, crank arm and bottom bracket, etc.) is it proper to grease the surfaces that will fit together, or not?
if you are using a high-end aluminum-shell BB, then get the "press-fit" specific Loctite and use that. this stuff is made for press-fit applications and holds well without any creeks. I put it in for my Cervelo R5 and a ceramic-speed BB and it is perfect over 3 years later. If you are using those cheap, plastic cups, then grease and go.
I can't imagine any reason not to lube a part that's going to be pressed into place. It will make the pressing easier with less damage to the materials and there's no way it will lead to the part sliding out somehow. Parts that are designed to be pressed into place need a whole lot more than lube to be pushed out of place.
If it helps any, I replaced a press-fit bottom bracket on a carbon-framed bike last year. So, such a thing definitely exists.
I wasn't going to lube it, but when I removed the old (factory) bb, there were traces of grease down there, so I cleaned and re-lubed it.
Before I did anything to the bike, I did look around for some guidance on what I should be doing, but found nothing.
To get to the bb I had to get through the crank, which was pressed into place - it was a bit more of a no-brainer to lube that along the way as I think the advice is a bit more consistent (although I used a different lube).
The crank arm should definitely be lubed before installing into a bottom bracket. This is because of the long term rotations that are going to occur, and you want cranks to spin as freely in the BB as they can.
As for other things like BB into the frame and headset, the reading I have done doesn't indicate that the BB needs to be greased prior to installation like you would a threaded BB; nor do headset cups into a headset. Park Tool have a couple of good tutorials for these two items (http://www.parktool.com/blog/repair-help/bb90-bb86-bb92-etc-bottom-bracket-service & http://www.parktool.com/blog/repair-help/threadless-headset-service)
Ultimately the reason you don't need to grease/lubricate those items at installation is because they don't move within the frame. The bearings will move inside each of the items. I.e. BB bearings rotate inside the BB shell and you will install headset bearings inside the cups. So it is the rotating parts that you would grease.
The reason threaded BBs should be greased is to assist in the installation of them as the rotate into position (i.e. thread onto the frame).
So ultimately there is no need to, however it shouldn't cause any harm if you do grease them before installation.