I had two 4d Ultrasounds in my last pregnancy. One I paid for as a keepsake and do not regret it one bit. I will do it again this pregnancy as well because it was the coolest most incredible thing ever.
I can't link to the photos here but I will be happy to pm them if you ask.
I will share though some more detail here. I had the first one around 27 weeks. It was done on a GE Voluson. You could see everything, including my placenta, the cord and all three veins. You could see it all. The baby slept through most of it. It was done in real time and we could see her sucking, smiling, and punching the placenta at times. We had a 30 minute appointment. You would be amazed at the detail.
The second one I had was about 32 weeks along. There was a new ultrasound tech and she was training on the machine. Because of my uterine anomaly they wanted to check out the position of the baby because I had a lot of pelvic pain and pain about where my septum is. I told the lady I had had a 4D and she asked if I minded if she "practiced" on me. I told her "Sure".
This one was about 15-20min long. The baby was bigger and weighed about 4lbs. (fairly acurate based on her birth weight) Baby was head down and we could see she had HAIR, lots of it too. It was harder to get full pictures of body parts because things get cramped in there. LOL We did get some really great face shots of the baby and they look exactly like her. It was amazing how much detail and likeness to her there was to the day she was born. In fact one of those pictures is framed in the nursery and some people think its a sepia picture of when she was born! We could see she had dimples too. You could see the dimples in her hands. She also smiled a lot!!! You could also see her private parts clearly. There was no doubt she was a girl! One of the cool things is that they can color code the umbilical cord and you can see how it lays around the baby.
It was something really special for me to experience. I really can't express how wonderful it was. My only regret is that I did not bring my older children. We will this time. We did get a DVD of real time video of the baby with my 27 week 4D US because I paid for it, but not with the latter one. So my kids did see that.