What similarities are present between Macbeth and Lady Macbeth other than their ambition?

In Shakespeare's Macbeth, feelings of
guilt are another trait that Macbeth and Lady Macbeth have in common, though they feel
them at different times.

In fact, the Macbeths experience
role reversals during the course of the play.

Macbeth feels
guilt before murdering Duncan.  This is itself a role reversal, as Macbeth reveals
emotions usually associated with females.  In Act 1.7 Macbeth first worries about the
consequences of murdering King Duncan, but he also feels badly because Duncan is his
kinsman, and Macbeth is his subject.  He also feels badly because he is, at the moment,
Duncan's host, and as such he should be concentrating on protecting his guest, not
assassinating him.  He feels badly because Duncan has been a "meek" king, and has led
the country blamelessly. 

Lady Macbeth, before the
assassination, doesn't worry about the consequences, and seems to feel no guilt.  She
pleads to be unsexed--made more like an aggressive male--and manipulates her husband
into killing Duncan.  When he obsesses over the blood on his hands immediately after
killing Duncan, she ridicules him and tells him "A little water clears us of this deed"
(2.2.70).

Yet, once the assassination occurs, Macbeth loses
all sense of guilt, and Lady Macbeth suffers so much from guilt that she ends up a
suicide.  While Macbeth kills the grooms, orders the killings of Banquo and Fleance and
the slaughter of Macduff's family, Lady Macbeth suffers.  She sleepwalks, ringing her
hands (obsessing over imaginary blood on her hands) in Act 5.1. 
And she commits suicide later in the play. 

Ambition does
unite the Macbeths, but so does their guilt.