Yes, my full round was built with them. I have 265 current customers since August 2007. I have had 7500 leaflets dropped and in all I got over 320 customers. As usual with any new round about 20% dropped off after a few cleans but I was still left with 80%.
For me it was about 4.25% response rate, however, you can cover far more ground with leafletting than you can canvassing. You can also leaflet at any time you like(within reason) where as you can really only canvass with any success when you would expect people to be home from work.
Personally I think the success of this leaflet is that the customer has to make a decision. I say on the leaflet I will be back within 3 days, they then need to make a decision rather thn throw the leaflet in a drawer and forget to ring.
I have posted a copy of what I use below. I know it is very simple and not very pro looking but I know it works for me.