Had one at about 28 weeks - it was expensive, but it was worth every single penny - Think we paid £200, 45 minute dvd and 6 pictures. Got to take my parents and my sister with me as well as dp which was really nice.. Infact once the rugby has finished I might watch ours.. havent seen it since ds was born 21 weeks ago... No time!!
i had one at 24 weeks, which was a bit early - she looked like a mask, as she was lying the wrong way and so all I saw was the front of her head and then a horrid gaping gap at the back, which was just the imagry, but it was horrid. make sure you get the optimum time to go.
Mine was only 30 dollars (10 quid), most of it was in 2D but some of it was 3D so got 5 3D pictures and a DVD of the whole scan. Was at 20 wks. SOme of the pictures are on my profile. I think she looks beautiful though other people seem to think she still looks a bit alien-like!