I definitely had one, and I question any "research" showing they are unsafe at normal levels. I think that's the key- I do think that if someone is goofing around, or the scans were performed 30 years ago at much higher powers, there could be higher risk. There's no evidence for "cavitation" when used as it is for diagnostic ultrasounds- it's all about the power used. It can be risky if used incorrectly. (I'm familiar with a group here that actually does cavitation research, it's really interesting, actually!)
Dopplers used to listen to the heartbeat actually emit a more intense beam of energy, but over a smaller area. I would seriously question anyone resisting one normal ultrasound scan who gets a home doppler unit that they use often! I think home doppler units are a much higher risk than a routine u/s performed by a trained person. I know if I had one I'd be tempted to use it too much- I'm sure that is a common temptation!
Of course ultrasounds are not perfect, and miss defects, etc. I think they are important because they can detect at least some problems- and some of those might be able to be either cured or at least mitigated by treatment. Placentia previa is a big deal, and I strongly disagree with the mothering magazine article that "oh, only 1 in 20 is a problem". Well, that's a HUGE risk to me. The way you know if you have it is if you develop serious problems and/or have a miscarriage! I think the relative risk here is clear. I know some people resist any and all interventions, but intervention-wise, this one is not up there on the risk scale like some others (CVS, amnio) are. We decided not to get the triple screen because I would never get an amnio- that risk, to me personally, is too high, and due to my weight, a false report on the triple screen was likely. So I understand the idea of resisting testing if it leads to something that would be a true intervention with documented risks. I think the u/s can be of even *more* use for someone choosing homebirth, as at least some problems that may be an issue can be found beforehand and you can be prepared. I think they key is understanding the limitations of what u/s can tell you before you get one.
Saying all that, I don't think it wise to get one just to see the gender (unless there is a sex-linked chance at a genetic disease or something like that), and I certainly don't think it's wise to get one of those 4-D scans in the mall. That should be illegal, imho. Who knows if the dude in the mall is doing it right?!
Even if you would never, ever get an abortion, I think knowing in advance of any problems (and solutions of those problems) is certainly a very useful thing to have, and so a routine u/s at ~20 weeks is a great idea. If there are no problems, you probably never need another, as the midwife/doc can tell the position of the baby by feeling, etc, when you are much farther along. Just my opinion. I was nervous about cleft palate due to the asthma medicine I take- as sparingly as I can- so it was a HUGE relief to see that that hadn't happened (I just had my 20 week u/s on monday). I didn't think it would be as big of a deal, but it was very big to me. I felt much more relieved than I thought I would, and the reduction in stress from that- along with seeing it move like crazy- I think can be a big positive in a pregnancy, too. I know my husband and I sort of bonded to it by seeing the u/s, which was quite brief (15 mins), actually- and so for us, it had an additional plus side. You can see so much more on the screen than you can on the little pictures- it was absolutely fascinating.
Of course this is my opinion, but do take unsubstantiated claims about the danger of procedures with a grain of salt, along with the normal grains of salt about all the "safe" ones too! It must be absolutely devistating to have a child with a birth defect and not know the cause- and let's face it, I think most times they don't know the cause- and it's tempting and very human to want to blame something- anything- for it. It's very understandable, and everyone has to make their own decisions. I take the articles on mothering with a large grain of salt- (the one about pot smoking really, REALLY put me off). Good luck with your decision, and with your u/s if you get one!