Just a tip. The otherday I found these:
http://intranet.cs.man.ac.uk/mentors/resources/broada/cs/cs710/viva.html
Viva questions. Useful though for any stage of your Phd. If I feel as though I am losing track, I go through these and try and answer them as quickly as possible. Helps to get you out of that 'woods and trees' syndrome.
Of course some of them I can't answer, but those are perhaps worth spending more time thinking over (if they are relevant), or perhaps you could discuss them with your supervisor - though if he's anything like mine he'll just tell you not to worry about them!