Hurt,
How important is it to be truthful and completely truthful about ones past in a relationship?
To a degree I can agree with Sentinel if there are issues such as she mentioned involved (children, AIDS, etc). BUT...for what I guess I'd call "non-essential" or "non-critical" items like your past boy/girlfriends...I say no.
First, anyone who wants to know about every detail of your past romances has problems with insecurity, especially if they want you to "trash" them in his/her presence. Telling them makes you feel bad (one, feeling residual loyalty toward them, two, if it's used to make you feel bad because of your choices back then) and doesn't help this other person either.
Second, picture two people who feel adamantly that there should be total honesty, no secrets, etc., between any two people. So they're talking one night and one of them says, "You know, I could never stay with a person who had (insert worst past activity you can think of here)..." and guess what?
So right away you're torn between your just-expressed feelings about total honesty and your desire to make this relationship work--may feel this is the one for you--so what do you do?
So I don't feel total honesty is workable in these situations. But I also feel that, as Spock once said, "To withhold the truth is not to lie." IOW, if you don't ask about any past criminal history of mine and I don't volunteer the info, then I haven't lied. If you ask and my answers get more and more dancing-between-the-raindrops in trying to answer, even if you don't get the answer you dread, it's safe to assume that where there's smoke there's fire...unless I can give you a very good explanation for my evasions, one you're willing to accept. One might be a signed confidentiality agreement, especially if I held a security clearance, but otherwise....
Hope this helps you some.