I contacted the e-mail address and got a response.
It is on the event list but the date is for next year, they are going to amend that and confirmed it was 8am on Saturday 20th November 2010 (not 2011).
There is a map on mapmyrun called york unofficial marathon - that's the route. There are no marshals, water stations, tee-shirts - well anything really. It seems you are responsible for following the route or making your own one up! I looked on the map and there are some shops you run past where you could buy water. So it looks like it is just a bunch of runners that have set a route and are running it. I'm definitely going to turn up, what can go wrong!!!
He or she (they gave no name) did say that there is a pub next to the Museum Gardens where they are thinking of going to afterwards. It gets better and better!
I was also told that this was only dreamed up this week but they have had a few responses of people running some or all of the route.
Anyone else up for this?