Thanks for the comments.
Mick, I see what you are saying about the 'fun' element. Although I have to say I really did enjoy the first 6km of the race on Sunday. I had a couple of quick exchanges with a few people, but it was more the feeling of being part of something which other people were also doing. Maybe as/if I improve this will become less important to me, but for the moment I think I'll look for similar events. I did like the whole feeling of the run, and certainly wasn't thinking of it as racing anything other than the clock. I really see what you mean there.
It's good to hear you don't think a half is beyond me. I know I'd be slow, but my stamina is fairly good. I've had a look at the Engligh one in Warrington, although I'm slightly put off by the fact the first half is uphill.
Flo Po - you say my speed will improve as I up my distance. Do you think it is best to focus on increasing distance for the moment rather than trying to do anything specifically about my speed? My vague plan was to keep with the 2 short runs each week (about an hour each, usually one with some sprints or hills) and gradually increase the distance of the long run at the weekend until I'm running for 2.5 hours fairly comfortably. But i wasn't sure if I needed to be more structured on speed work.
Victoria - Good Luck!