There's an episode of House where this is nicely demonstrated by House and Wilson trying to figure out if Cuddy's daughter has swallowed a coin. On ultrasound it might be a dime, or it may just be an air bubble.
While I've heard that some House episodes are very educational, I can tell you that that House episode was just another medical TV show keeping the public sufficiently ignorant of medicine to ensure that we'll always need health professionals. What the HELL were they doing getting an US!?! I work in an emergency department and anyone with eyes can tell the difference between a foreign body and an air bubble on an X-ray. To my knowledge US is never used to evaluate for foreign body.
Wikipedia: http://en.wikipedia.org/wiki/Foreign_body_in_alimentary_tract
GI tract example: http://emedicine.medscape.com/article/776566-overview - Is it a nail, or an air bubble???
However, just because US aren't useful for evaluating foreign bodies it doesn't mean that the technology isn't extremely promising for other factors of disease or (in the case of the article) complications with pregnancy. Can you imagine if these were widely available how easy it would be for a soon-to-be mother to learn the basics on what to look for to prevent a serious complication? Think about how many books and media a pregnant mother reads and intakes to educate themselves on pregnancy to ensure they have a healthy 9 months? If a 3-hour class was offered to mothers about how to look for an US complication and a hand-held US machine was loaned to them for their pregnancy, I'm confident that nearly all would jump at the opportunity. It wouldn't be training them to diagnose themselves or their babies with any disease it would be like, "If you see your baby's umbilical cord wrapped around his neck and you feel funny, then you should probably come see the OB/GYN immediately." That's something you could teach in a 3-hour class.