My brother predicted a 10Hour Ironman, with a phenomenal bike split - I think he wanted to do a 5 Hour bike, or 4 Hr 20 (which is like world class). In the end, bike wise, he came in 10 minutes under my time, and managed to swim about 8 minutes quicker, and run about 40 minutes quicker. That means he spent 20 minutes longer in the transition areas than I did, presumably having a small picnic, with wine glasses and cheese crackers.
While he did much better than me in terms of finishing his first Ironman attempt (I got sick before my first two attempts, and actually got ill before the third as well), he seems to have made a few pretty big mistakes, like not 'going the distance' before the actual event, not doing a 180km bike ride to see what effect it has, and not doing a run longer than 21km.
I'd like to be able to stand on the beach in PE mext year (2009) and see if I can improve on my time, and also get an hour or so under his. Anything is possible ;-)