To be, or not to be...*
I'm not sure how to alleviate PhD despair (sorry Ceri), but I've made great roads into defeating dreaded PhD procrastination this week...by using a timer.
The idea is that you set a timer (I use my phone) for a few minutes 'on,' during which you focus completely and obsessively on the task at hand. As soon as the time is up, you allow yourself an equal amount of 'off' time (I knit). I appreciate this wouldn't work for everyone, but I've found it a really useful technique for dealing with writer's block.
This site recommends 8 mins on/off. That works just fine for me.
* Hamlet was, of course, le procrastinator par excellence.