We know that the wizarding world has laws about keeping things secret from Muggles, lots of laws and all sorts of protections. We also know that there are loads of Muggleborn and half-blood wizards and witches. So the question is this - how do we reconcile these opposing ideas?
JKR gives us very little in the way of information on this. We hear a bit about both Harry and Hermione's experiences with their families (but not nearly enough about Hermione's, and Harry's is colored by the fact that the Dursleys are OMGWTFNO about the wizarding world). We know about Tom Riddle Sr's reaction to Tom's mother being a witch, but again, this is colored by the fact that she was using a love potion on him. We know about Seamus Finnigan's parents, but only in that his father was surprised to find out.
What I'm wondering is this - how do you handle getting to know a Muggle intimately if you're a witch or wizard? You're not allowed to tell at first, and there's nothing in canon to suggest when you're allowed to reveal the truth. After you're engaged? Married? Do you have to get permission from the Ministry first? More importantly, what does that do to the relationship? You've kept this secret for months or years, and suddenly you have to tell the person you love that you aren't who they always thought you were - and it's a rather shocking secret to have kept, considering Muggles don't believe in magic.
So... there it is. Thoughts? Feel free to pimp this out - I'm quite curious as to what others think.