I'm not mormally one that worries about time. However, I do record every run to help asess my fitness levels.
I have checked my spreadsheet and compared my longer training runs (8 miles or more) against my race time and found that the race time is approx half a minute quicker per mile. That must be down to adrenaline and atmosphere.
I've only done one race as yet, but it's interesting I did seem to go faster on race day (even though I had to zig zag at times get past a lot of people!)
EG, my 5k split for the Great Manchester run was 29:25. Today I decided to run a 5k at a pace I thought was a lot quicker, and would produce a substantially quicker time bearing in mind I didn't have to save something for another 5k on top, but I ran 29:15! Obviously some work to do, unless I was still a bit tired from Sunday...
The first time I did 10k in training I did 1 hr 07, and got it down to 60 minutes a week before my first race, then ran 58 12 in the actual race, so adrenaline and atmosphere must definitely play a part - as well as having plenty of people in front to keep aiming for :d