I have and I would. Anyone who does want to is BI, not necessarily someone who wants it up the ass, but they are BI. My girl knows, we are monogamous, and she is cool with it as long as I am cool with her digging chicks; however, I would fuck my girls ass way before any of these shemales. She has a better one and knows how to work my cock.
Just find a feminine, petite girl who prefers getting fucked. You will be shocked how girly she might be in the sack. If you find the right girl, not only will you have no regrets but a whole new world of females will be opened up to you. I love fucking T-Girls and I feel just as straight and masculine fucking them as I would being with a girl that had a vagina. If everyone here were to allow themselves a "1 Tranny Mulligan" many would understand why people enjoy fucking tranny ass.
Honestly, the results don't really surprise me one bit. My girlfriend used to work in a videostore years ago and they had an adult section. She said the people primarily renting tranny porn were essentially what you'd classify as "straight" guys. Gay guys didn't touch it because well why would they? They like guys not guys that look like women.
Also, from my own personal experiences running my websites and seeing the google search patterns there's a huge group of people who are into this stuff.