I'm thinking that there are 4 things you need to be able to do if you want to do an ironman: an all day intense aerobic workout, be able to swim 2.4 miles, be able to bike 112 miles, and be able to run a marathon.
Whenever someone would tell me I should do an Ironman I would tell them that there is no way I could do the run, after today's run I am thinking this is doable. I know I can do an all day event, I know I can bike 112 miles, and now I am feeling confident that I can do a marathon. Next step is to find a place to work on the swim. I am not worried about open water swimming, as I have done a lot of swimming after the Jetski in nasty weather, and scuba diving in the ocean waves, but I really have never swum for distance and so I have no idea how hard 2.4 miles is.