Well I did the run and it all went well. I finished in 48:28 in 545th (out of 11,000). Quite a few runners dressed up in costumes so a variety of superheroes, fairies, smurfs etc. I didn't spot any Discworld characters - perhaps I'll have a go at one of those myself next year - I quite fancy running round as Captain Carrot!
It's not too late to sponsor me and give some money to the Alzheimer's Research Trust: http://www.justgiving.com/kafox2010
And up to my £400 fundraising target I will be "Matching it for Pratchett" with my own personal donation to the Alzheimer's Research Trust, so your donations will be doubled (more so if you are a UK tax payer as Gift Aid can be used as well).