Of course, like others have said, women lie too. Everyone lies sometimes. Apart from all the reasons already given for why men, specifically, might lie, I would say that one other reason is to protect themselves and the person they are lying to. Not just fearing the consequences of the truth, but simply being unable to admit their own failings, weaknesses and NEEDS.

This whole thread runs the risk of being sexist in the most important sense of over-generalizing to the detriment of both sides. However, I would say that most men have a lesser ability to articulate needs etc which might lead to actions kept secret - though the actions might not be anything particularly worth the subterfudge. Still, if someone keeps something secret one automatic conclusion to jump to is that it's significant and therefore OUGHT to be shared with a partner.
Maybe and maybe not.

All depends on the lie and the reasons for it. This is probably no help at all...