Well, I do not know what use it could be for. Generally, a "fair" is a type of gathering where there are displays, games, and food. (Definition from dictionary.com: An exhibition intended to inform people about a product or business opportunity: a computer fair; a job fair.)
This does not work as well with PDA's (Personal Digital Assistant) because it does not require a social gathering. Also fair is normally used as an adjective.
Enough of the english lesson, it's a short enough domain but it really confuses me. Unless you can find a great way to use this domain, I don't think it would be worth much more than reg fee. If you develop it well, it could be worth a few hundred dollars (depending on a variety of factors).
If I'm wrong about the entire PDA thing, I apologize. I'm sure PDA could stand for something else.