Here's an older thread on the subject.

You can also review the Ironman Foundation's latest Form 990 yourself here. They have most, if not all, of them on their website. From the latest filing you'll that they had $3.23 million in contributions, grants and other revenue. From that they gave out approximately $1.66 million (51%), had administrative expenses of $930,000 (29%) and essentially retained income of $640,000 (20%).

You'll have to decide for yourself whether this is acceptable to you.

My understanding is that IMF raises money and then forwards it to a charity. So the money is 50 percent less than what the charity would get had you given it directly. Why wouldn't you just find out which charity you want to support and cut out the middle man. I don't give to umbrella organizations that raise money for charities for this reason. If you want a slot on a sold out race buy a foundation slot and be happy that some of the money goes to charity.

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They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

Exactly!! Below are their financials for 2015. Not to pick on just Ironman Foundation, but most charities take a very liberal view of what counts as "program services expenses" so the reality is that much less than 70% actually benefits the end program. There are a lot worse "charities" than the IMF, but there are also a lot better.

The Ironman Foundation, Inc., Tampa, FLRegistration Number :CH44958Expiration Date : 7/27/2017Revenue Source : 08 - IRS 990 w/ Sch.A and Audit (12/31/2015)Total Revenue : $3,234,857.00Program Services Expenses : $1,899,787.00 73%Total Expenses : $2,594,438.00Administrative Expenses : $252,256.00 10%Surplus/Deficit : $640,419.00Fundraising Expenses : $442,395.00 17%