Don't know if this is too late to reply. We joined this year and are just about to do our first house swap, plus have one lined up for next year. I think you probably have to be a bit open minded about where you go, but £ 30.00 per year for all your UK holidays seems like a good deal to me.
We are in the middle of it at the minute so can update.
1) We are staying in a house with full cooking and washing facilities that would probably cost at least £600 p/w to rent
2) Internet access included !
3) All stuff for DS here so much less to pack
1) Interminable cleaning before going then guilt crisis in case not clean enough
2) Not quite as relaxing as being in a cottage or hotel as we are in other peoples belongings so doesn't feel quite as much of a holiday
3) It was only when we got here that we realised how much we had done on trust. Luckily everything is great here and as described but probably worthwhile sending lots of emails detailing what is in the swap in case of any legal problems
All in all I'd recommend it - plus our cooker is clean for the first time ever
We've done 17 all with the NCT. With the exception of one,(which was the people's holiday house, not their proper home) which was quite dreadful and not described adequately,deprived area, washing facilites promised in description but not there,damp, smelly, bedside lamps unwired, door handles missing, altogether a deeply drpressing experience) we have had some of the most memorable, quirky and satisfying holidays ever. All based on trust which makes it even better. Loads of cleaning beforehand, but you always come back to your house as you left it. Lovely gestures sometimes, sweets on children's pillows, we even had someone paint the front of our house(luckily it is not displeasing)which was the most personal, kind gesture we've ever had. Think about it, free holidays bar the £30 annual subs fee. Couln't reccomend it enough.