ive fucked 3 GF's in the back. 1st one, was high school GF, we had been sleeping together 2 yrs so the normal go round was getting a bit boring. I asked, she was cool with it. Went slow til i could see the look on her face that she was enjoying it and not in pain. than went to town on her.
2nd girl was prolly my 4th GF. meet her on spring break in panama city so we did all sort of crazy shit. I went to college at western ILL, she went to a small school in eastern Iowa. same as the 1st, I asked, she said yes (she had already done it with her last BF) and i went slow til i knew she was enjoying it. then beat her up good.
3rd. the GF i have currently, she doesnt like it. I have to start with a finger to warm her up a bit, then use my unit on her. I know she doesnt hate it but i only get to do it once in a while. And the next day i am stuck doing all sorts of favors for her.
Overall its fun(esp for me), some girls dig it others not so much. if your girl is new to it dont pound her shit, it will be the one and only time you get to put it in her ass.