How important is Lady Macbeths influence over Macbeth during the play?

In Shakespeare's Macbeth, Lady Macbeth's influence over Macbeth is vital.  She is probably the primary influence that leads to Macbeth killing Duncan.

The witches heavily influence Macbeth, too, but they only predict to him that he will be king.  Both he and Lady Macbeth turn that thought into a much more dangerous thought:  you will be king, now, and you will get the throne by assassinating Duncan.  Eerily, Macbeth and his wife take just a few seconds each to turn the thought of the prediction into the thought of assassination.

Macbeth falters, of course, and Lady Macbeth manipulates and ridicules him, questioning his manhood, and talks him into continuing.  Her influence is vital and primary.

At the same time, though, though she is the primary influence over Macbeth, Macbeth is even more to blame. She is only an influence, he is the murderer.  Niether the witches or Lady Macbeth actually do anything.  Macbeth does.  He is the killer.  Lady Macbeth has an opportunity to actually kill Duncan herself, but she can't do it for sentimental reasons--the sleeping Duncan reminds her of her father.  Macbeth can do it, and he does.

Thus, saying Lady Macbeth is the primary influence does not remove Macbeth's responsibility.  His own ambition is central to his actions. 

By the way, the play really doesn't show much of the relationship between the two Macbeths after Act 2.2.  Macbeth shuts her out of the decision-making process and as far as the reader knows she has virtually no influence on him the rest of the play.  She continues to berate him when he acts foolishly in public, but she plays no part in any of the murders except Duncan's.