I'm in too! I am fairly new to running, but having lost a load of weight over the last 18 months I am now hooked on it and its getting me through a plateau as well as toning me up and getting me fit!
I decided to enter the Reading Half because I wanted something big to focus on and aim for. I have done a couple of 5k races and recently discovered ParkRun too which I loved. I am doing Reading as a golden bond place with Leukaemia & Lymphoma Research as my Mum had Lymphoma cancer twice and is currently in remission again.
I have no idea what time I am aiming for, and may have to walk a little of it, but I am not really bothered as I am just doing it for the personal achievement of running a half and for the charity. I did put my 5k time into the race calculator weeks ago and it gave me a predicted time just under 3 hours!!! But since I did that last 5k I have reduced my walks and increased my running time so I think that a time of somewhere between 2hr30min and 2hr45min will do for me! I am currently following a BUPA half marathon training plan and its going really well. I can feel improvement almost every week and as I keep a running diary now I can look back and see my times improving 
Hope to see some of you there... I'll be one of the ones in a bright yellow LLR running vest 
BBxx