I feel your pain. This is the thing that's worrying me most - more than the birth! 
My PILs live abroad, they mean well but my MIL can be overbearing and my FIL quite hard work. MIL insists she wants to come when baby first arrives as I will need 24hr (!) practical help. She thinks this based on what happened in her own family so sees it as a non-negotiable duty.
Frankly, I can't think of anything worse! My own family live nearby, are amazingly helpful and won't interfere, and DH is brilliant, so I'll already have plenty of support on hand. Like the rest of you, I only want to see people for a couple of hours at a time max. We have a small house and it can be really intensive having PILs to stay under normal circumstances. I've convinced them it's going to be too much of a squeeze if they stay so they've sorted out other accommodation, but MIL still intends to be there at the crack of dawn so she is 'on hand'. Her parenting philosophy in no way chimes with mine, and I can imagine myself just holing up in the nursery to avoid her and try and establish BF in peace.
All I really want is to have those first few precious days with DH and the bub on our own (most of the time, anyway), esp. as DH won't get that much time off work. I know as grandparents it's really exciting for them but I do feel it's imposing too much.
I've asked DH if he can try to limit the length of their visit and manage MILs expecations of lengths of visits each day, but he's afraid of upsetting her and says we should just deal with it when it happens...gah!