Yes we have done two now, enjoyed both of them and are planning to swap again with this years swapees in 2009 despite them having diabolical weather all the time they were at ours.
Fantastic for children because they will have toys at the other house, if you can try to pick a family with similar or older children.
Cleaning and tidying up beforehand is a pain but think of it as an annual spring clean, certainly the only time our oven gets cleaned. Tidying up to leave again a bit of a pest but we were pretty speedy this time.
The website has photos of some of the houses so you can see before you go, might be worthwhile as this years swoppers said that this years was the best swap they had done and I don't know if that was down to the quality of accomodation that they had before or not.
Also good if you want to stay somewhere that isn't a touristy destination because you have friends there like we did this year. Means you are not imposing on your friends for too long. Last year we swopped cars at the airport as well.
Its kind of weird as you get to know a lot about the family without having met them, but weird in a nice way.
We enjoyed it so much that we are thinking of joining an international network so that when rookietodler starts school we can still go on nice holidays abroad because we will just have to pay for airfares.
I say go for it, even if it doesn't work out its only £29.99 going to a good cause.