Mark,
How long term are we speaking?
I did 4500km in a dCi Turbo Diesel model last month in UK/Ireland... didn't have one problem. It seemed very well put together, no rattles or squeaks, didn't use any oil at all in that period - first service in Europe is at 30 000km!? A very relaxed touring car and great in the city too - very very easy to park. It was quite a busy time doing that much driving in 3.5 weeks so I'd expect if anything was going to go wrong it would.
My cousin's friend has a 2 litre Scenic RX4 they've had here for well over 6 months now and they haven't had any problems at all - actually they're delighted with it from what they told me.
The Citroen Xsara Picasso is definately more popular than the Scenic in Ireland and the UK but that's because it's cheaper.
By the way - how can there be long term doubts about the Scenic? There are literally zillions of the original "Renault Megane Scenic" which is 7 years old running around in Europe. The current model is the Scenic 2, which is a facelift - new multi-parabola headlights, high-jewel tail lights(WHO INVENTED that word?) , bumpers, wheel covers, 6 airbags etc.
It seems bizare the Australian media put down Renault because they're of their 'unknown brand history' but maybe we'll let AlanS take over on that one!!!
Derek