http://news.wustl.edu/news/Pages/13928.aspx
I did various forms of cardiac ultrasound research for 10 years at the med school. So, I know a little bit about it. It's easy to find your heart or a baby, but knowing enough to make any sort of diagnosis takes a lot of practice. No matter how smart you think you are, you won't be able to order one of these on Amazon Prime and find a leaky valve or a problem with your gallbladder. The images are noisy. Positioning the probe to get a clear view of the structure you want to see is an art. If you're obese, forget about it.
I'm all for disrupting the imaging industry with cheap hardware, but this article and a lot of the comments here show the general lack of knowledge about medicine. Have a look at the comments in the heart attack thread. Some people think they can just buy an ECG and self-diagnose a heart attack. If anyone spent twenty minutes looking at ECG's (or ultrasounds) with a knowledgable tech they'd cringe at how stupid they sounded. Ultrasound is the exact same thing.
Finally, ultrasounds are regulated medical devices. As far as I know, it's illegal to own one.
On a happier note, 3D ultrasound is kind of awesome. If you get a probe that can rotate 180 degrees, it is really easy to make a 3D model of the structures. I did it for a work-study job in 1998 on an old SGI indigo. Sadly, you can get much better pictures in MRI or CT so 3D ultrasound is not really used in the clinic (it's gaining some traction in cardiology, though)