Yeah, if I were to ever become, *cough* involved with a girl, I'd wait until my parents were, *cough*, gone.
Better safe than sorry.
That said, I have a little contribution to this thread:
I have not walked in on my parents doing "it" before, but in my old house their bedroom was right next to mine, and shall we just say I hears some interesting things in the middle of the night.
I have also walked into the bathroom of find my mother examining, *cough*, herself in the mirror, and I was promptly given a whack in the face coupled with a boot out the bathroom door.
Hey, it's not my fault she never locked it!!
(God I hope I never see/hear those things again!)