Hi Runnermum,
Im back again... I will always back cloth, DD has been in cloth full time from day one and has never had a sposie on, so i am biased (but DSS was in them and i hated them on him)... but thats not what i am doing back in here adding a few more cents to the debate.

I was reading an old issue of My Child (Autumn 04) Anyway there is an article in there that is called 'the nappy revolution'
There is a bit in there that i think will be of interest to you, seeing as you are leaning towards the sposies but are conscious of the environment

Sinead Roberts, co-founder of Eco Direct begain importing Moltex Eco Nappies two years ago. She says 'The nappies contain no fragrance or lotions, and aren't unnecessarily bleached, so they wont aggrivate fragile skin.' The outer later is made of biofilm, wich is 100 percent degradable, and they are chlorine free'.
I tried Moltex on Henry overninght and there were no leaks. They are silky smooth and reliable in terms of absorbancy and containment.
Roberts adds Moldex Eco Nappies are also compostable 'You can put your wet nappies into a worm farm and they will break down within eight to 10 weeks, providing lovely fertiliser.' They are available in four different sizes from Eco Direct
If i ever went to sposies i would find these and have a worm farm - it makes sense, rather than contributing to landfill

Hope this helps/is useful