I was all costed up and quoted out, poised with pen and chequebook to sign up on Friday last week when the news broke. My installer (the one with the best quote - £3.50/W and the one I trust most) cannot deliver by the 8th Dec so the deal is off. Second choice is more expensive, can deliver, but I have some reservations about the over budget quote and I have lost faith in the gubbinment not to pull out the rug in the future when paying that price.
Being a slightly more complicated install, mine would have been at the more expensive end of the available spectrum. Break even on 43.3p FIT vs another investment available to me for the same money would have been around 14 years - note, this is not the same as "paying for itself" which would have been 8.5 years, but reaching the same actual capital+return values. At 21p, it comes in at over 21 years with generous assumptions!
I suspect the thing to do is to wait until the costs fall a lot more, as indeed they will, so that the installation is cost effective on a lower and sustainable FIT, if a FIT is still necessary.