Our solar thermal water heating has worked well - negligible gas consumption for approx. 4 months of the year - we have learned to 'work with' the system, taking advantage of good heating days to get the washing machine on. We were one of the PV pioneers and consequently don't get the higher rate FIT - we have recently signed up with Ecotricity,though, who pays us 16p/kWh for everything we generate. We are also having another set of PV panels installed to benefit from the new FIT.
I am a retired engineer and as such haven't been able to kick the habit of monitoring each and every energy saving / renewable energy measure we have taken. I have logged information from our utility bills going back 30 yrs and for the last 5 yrs have made a point of taking weekly meter readings of water, gas, mains electricity and PV electricity (now log my readings on 'imeasure'). The latest addition to our armoury of energy efficiency measures was under floor insulation in our lounge - can't wait to see what effect that has had!
I am presently Chair of the Renewable Energy Club-Warwickshire - we hold monthly meetings on a wide range of topics with invited speakers.