I've been fortunate enough to catch this hatch a couple of times. Last year it was epic during the week of July 4th, from Kirby Ranch all the way to Hebgen Lake. There were times when i had 10-15 of the big nasty fellas crawling all over me. It's equally creepy and exciting. The fish usually take the smaller yellow stoneflys (size 8- as opposed to the size 2's) but casting the big bugs is fun, and when a trout takes one it can be a thrill.
It is one of those spectacles, like the green drakes on the Beaverkill, or tricos smoke columns on the Missouri, or Hendrickson spinner falls on the Delaware that every fly fisherman should witness at least once.
I agree they taste like dirt, and yes i have.
Agust