My wife is back at Children's Hospital, this time with the baby (and toddler in tow; I'll be picking him up later). Although he was fine when we brought him home, he had been spitting up more and more, to the point where he was forcefully spewing not long after every feeding. We had planned on waiting to take our little "fountain of youth" to the doctor at his regularly-scheduled appointment tomorrow, but it had gotten bad enough that we decided to go ahead and make a call today.
My wife can't remember the exact name of the condition, but after a quick google, it looks like pyloric stenosis. They have him hooked up to an IV already, and they are scheduling him for surgery sometime tomorrow. According to the doctors, this is a very safe (and non-emergency) surgery. If he gets a morning appointment, he could even come home as early as tomorrow night.
Although I'd rather not have to go back to the hospital, at least it should be a pretty short and uneventful stay; and after this, my wife may not have to bring several changes of clothes (for the baby and for herself) everywhere she goes.