For our local iron distance event (www.redmantriathlon.com) we've had the aquabike for the HIM distance, and I'm pretty sure we are adding the option of the full IM distance this year. Unfortunately, none of the other shorter races around here offer it.
I did the half IM aquabike last year and I LOVED it. My running had suffered and I was in no shape to do 13 miles (even walking). It was great hammering like all h*@l on the bike and then getting off and being done. I'd love to do it again sometime.