Please dont think I'm stirring things up but thought I'd add my tuppence worth....
The only experience I've had with LPG converted cars is during training with Herts Fire and Rescue. If a vehicle is known to be LPG converted and is ablaze, we have to maintain a distance of 500 metres (Yes you did read that right!) The training material we've seen involved a car alight in the middle of a field, test coniditions etc and when the valve began exhausting, the pulses became more frequent (shown as bursts of flames similar to a flame thrower) and when the tank eventually went up, it blew the camera and camera man right over. Remember this was in the middle of a field. Same applies if the vehicle is in a car park, or motorway pile up, 500 metres.
Im fortunate enough to walk to work, and town and probably only cover 50 miles a week so LPG would never been an advantage to me, and the general feeling among the Fire Service is the Government was CRAZY to allow it to be used. All i ask is if you have young kids that you strap into the back of the car, dont go LPG.
Like i said I'm not lecturing (although it may seem like i am

), its just with my limited experience of LPG I am against it as a non essential fuel.
Saying that thousands of people are using it so each to their own
Good luck