Honesty:The best policy?

Nick Clegg, the new Liberal Democrat leader was recently interviewed by GQ magazine, obviously an attempt to raise his profile in the "right" circles. While admitting he'd had "no more than thirty" lovers in his life, he point blank refused to answer whether he'd ever smoked a joint.
Likewise, David Cameron, the Conservative leader admits to membership of the Bullingdon Club, famous for smashing up top class restaurants. But clams up when asked about any drug linked exploits, even failing to deny claims in a biography that he came close to being expelled from Eton for using cannabis.
Nick Clegg is well known for calling for honesty in politics, but only as much as he is comfortable with it seems. Do politicians think it is better to say nothing when confronted? That we will all forget in time, if they look at their shoe's every time they're asked?

For me this question should have two possible responses from anybody who has ever partaken, starting either- Yes I have tried it, but regret it..., or, Yes I have tried it, and don't regret it...

On the other hand I applaud Boris Johnson, Henley MP and Conservative candidate for Mayor of London. Interviewed on Friday he admitted to both snorting coke and smoking ganja, saying that "The stuff you and I may have smoked is not the same as the kid's are having now. I think skunk and this stuff is very, very dangerous......I thoroughly disagree with drugs. I don't want my kids having drugs."
Surely it's far better to openly admit to your actions and give your reasons why they are mistakes, that you now regret. This would give the public correct information, allowing them to make their own informed decisions.

I hope this takes precedent in the world of politics and other MPs follow suite.

What do you think, is honesty the best policy?