I have sold quite a few homes in the Permanently Affordable program. It can be a great way to live in a nicer home than you can afford on the regular market. Around year 2000 the city required all builders to build 20% of their new project in an affordable price range if they were to be granted a building permit. So most of the Affordable homes are newer homes (mostly townhouses or condos).
The buyer has to qualify by income and other items -- for instance they must be employed for a minimum of 30 hours per week. It is NOT for undergraduate students, but grad students have enjoyed these homes because they ARE employed as assistants usually. You CAN sell for a profit, but the maximum amount is determined by the city. The good news is that they allow you to sell for a minimum appreciation of 1% per year. Over the last few years, the approximately 2 or 3% was better than some other homes got.
I would be happy to go into more detail with you, and could refer you to some of my happy homeowners (and former affordable program homeowners who established their good record of payments in this program and then sold and moved to a market rate home).