Swapsitter - could it be global?

I've had an idea for a community project which involves setting up a bartering website. For more info visit www.facebook.com/Swapsitter The idea started out as a web based baby sitting club but has opened up to include a number of day to day tasks like baking, walking the door, house sitting etc.

I've read a few of the articles on here and would like to know if you think this is viable? The way I had planned it, was a bit like facebook where you have your own networks of friends rather than everyone joining the same group.

I might have 10 friends in my network and one of my friends in my group might have 5 completely different people in her group plus me. The common thread would be the points that we'd collect which we could then trade. My mum lives in South Africa and often says "I wish there was something I could do to help, but I'm too far away". With this system she could babysit one of my friend's children and "gift" me the points provided my friend belonged to a swapsitter group over there. Do you see any potential problems if everyone started with zero points and where ever possible, tried to keep using and spending them even if they're not staying within their own group? I don't want to get into a Zimbabwe $ situation where the points become worthless.

What factors would we need to watch to avoid crashing the system? I've heard that some schemes have been closed down by the IRD because of tax implications. I'm hoping that as the things people would be trading would be "good deeds" like babysitting that this would fall under the casual, friendly, not taxed area rather than having a business get involved and offer services in return for point. Bartercard and the likes can look after that sort of thing.

Any feedback would be gratefully received.