I am totally with you nicefleece. And some of these comments on here make my blood boil similarly. I do appreciate that people have paid jobs (please don't say "I work" as if those of us at home aren't "working" just larking around looking for something to fill our time - we work, we just don't get paid for it). I know that lots and lots of people have very valid reasons they haven't volunteered for the Fair. And also the events organised by the PTA, such as Fairs, aren't essential to the fabric of school life. But they are great fun for the kids, and the money they raise also goes towards buying other things that make the children's experience at school more fun. And more fun at school makes children happier to be there. Happier children learn better. All these people's children benefit from the hard work of a few people, and generally they are not remotely grateful for it.
The sad fact is that the people who do help generally are the ones who don't really have the time to do it. The ones that do often are the worst at not bothering. A lot of the people will simply assume someone else will do it. And eventually someone will. This doesn't make it right. Saying you are "too busy" is very rude - what you are saying is "my time is more important than yours - you may be able to fit in this event into your less important life, but I certainly cannot change any of my plans to help out as mine are simply far more important".
Some people do have genuine excuses. Paid work can be, but frankly not always. Maybe just one year you could take holiday and help out? Just for a change? I'm getting babysitters so I can help out with our fair - as my non-paid work has to be covered too, you know. Maybe you can't come on the day. Can you do something to help set up? Wrap presents? Help take it all down again afterwards, perhaps? Christmas is a bad time to be trying to get time off - but what about at least offering to help out at the next event at a less busy time? At least say thank you to the people doing it, explain why you can't help, and ask if there is something you can do which fits in with your reason.
Perhaps we should move towards a situation where only the children who's parents do actually help out are allowed to benefit from all the little extras provided by the PTA. Then we might see a bit more effort put in. "Sorry, you can't play with this new piece of equipment in the garden, your parents have never done anything to help out the PTA in anway, so you can't use it".
Of course I'm not serious. However, on a serious point, you should publicise everything the PTA has provided, I bet half the parents have no idea. And you should provide opportunities to help get ready for the Fair which are not during the working day, and ask working parents to help out then. And just get used to it. I've been on committees at playgroup and now school, and it's just the way things work. Very few people do all the work without any thanks from any of the majority of the parents, many of whom simply can't be bothered. A limited few simply can't help for genuine reasons - and, paradoxically, they're the ones who feel bad about it. Hope the Fair goes well!