I did an OB fellowship. I liked it and I still do. I learned a heck.of a lot of things. I did not think it was as useless as the people here who did not do one. In terms of job prospects, the demand is reasonable, but the locations are restrictive - not too many high risk centers in bucolic locations. You have to want to live in cities.
You get burned working your ass off to get complicated care plans in place for patients and obstetricians who neither understand nor appreciate the effort. Patients yell at you and insult you routinely. The nurses are never as highly trained as they should be and it's terrifying. It has zero respect for a sane schedule, but then neither do surgeons doing lap appys all night long. I sweat lawsuits all the time. You work closely with a service that understands zero critical care medicine, but is the "primary team." It's a hell of a lot of customer service and also a hell of a lot of "no good deed goes unpunished." I play constant intermediary between an OB side that understands no critical care medicine and an anesthesia team that does not really understand obstetrics. I have to work way too f-ing hard to convince my colleagues that most what they learned in residency in the 1980s doesn't really apply.
As far as I'm concerned, a chronic pain fellowship is the worst choice. I'd rather remove my eyeballs with a spoon.
TO ANSWER THE ACTUAL QUESTION: Yes, there isn't much information. You have to go to the sites and ask a lot of questions and talk to as many other interviewees and existing fellows as you can find. Otherwise go to SOAP - you can find nearly all the fellowship directors there. You can also crash the fellowship cocktail hour and chat. As of 2-3 years ago, the programs only filled to about 50%. I doubt it's changed much.