My DH is always horrified if I press too much but I tell him "you should see what the GP does!"
I usually just give the bump a bit of a rub and pat and say hello if it is pushing up a lot and it does seem to work. It works if I want to stir him/her up or if I want to calm him/her down. I think they quite like it.
I used to play the poking game when I knew it was a foot but these days all I see is a bottom poking up!
When the GP squeezes the head a lot to feel where it is, the baby HATES it and goes bonkers for a while so I think that bit might hurt.