Total honesty. Relationship builder or killer?

Tell me something you've never told anyone. What's the wildest thing you've ever done? You can tell me anything. Really.
Thats the question posed to Amy,a sweet girl next door by her practically perfect fiancée in "Sleeping Dogs Lie", an anything but typical movie I recently rented.
The subject matter of this movie (which was directed by BobCat Goldthwait of Police Academy notoriety) scares most people away from renting it, which is a mistake. As perverse and shocking as the premise is, this is really a touching, funny worthwhile movie. Your wondering what Amy did, aren't you. Well..once in college she blew her dog. She gave it oral sex. (gasp!) But they obviously don't show it and she never does it again. The point of the movie is whether she should tell the man she loves in the spirit of total honesty or if she should keep that one in the vault. All Hell breaks loose during a visit to her family home when the sins of the past are revealed. By the end of the movie, the lesson is that there are some things better kept secret.
I'm assuming most of us don't have a lusty one nighter with a Lab back in college to worry about, but we have done other things we don't want on the cover of the family newsletter. In order for a relationship to be healthy, how important is a policy of complete honesty?
In terms of kinky experiences and forbidden fantasies I'm confident I've told my partner all the kinkiest, which are thankfully turn ons in his case. Granted, theres nothing so wild as K9 lovin' in my history. I think it is a relationship builder that I'm not worried about him judging my past or my fantasies. I hope he feels the same way and from the things he has told me I think he does.
But are we totally honest with each other? No. If he comes out and asks me point blank about something my compulsion for being honest kicks in, but I don't volunteer anything that would hurt his feelings or cause unnecessary stress. I heard somewhere, as we probably all have, that if you feel the need to be brutally honest you are probably being more brutal than honest. I've had to check myself sometimes with my own brutal honesty to be sure of my own motives before jumping on my soapbox of Truth. I say I want him to be totally honest, and when I'm at my most masochistic you could swear I'm looking for something awful that will cause unneeded pain and suffering. Why else would I want to know what bad things someone may be saying about me, for example. I know I'm not alone when it comes to digging where I shouldn't be digging. But when I'm being rational I'm glad my partner loves me enough not to say some things, especially if they could only do damage.
So how do I feel about total honesty? Honesty and trust are essential to a healthy relationship. But when it comes to some truths...what he doesn't know won't hurt him.
What do you think about total honesty? As bloggers sometimes it seems like we have no limits in terms of what we will reveal, but what are yours? Have you ever put something out there that was obviously best kept in the vault? Has anyone ever confessed anything to you that you really wish they hadn't?