Interior trim falling off. Interior bulbs failing. Engine warning light at approx 60k miles, disapeared, came back at 65k, car now stutters and lurches on occasion, looses power and slows down when putting foot on gas, does not pick up until you floor it.
On the whole I have found it to be a great car to drive, it's comfy, stylish, plenty of power for a car of this type / size.
Servicing can be a little pricey, my last service was over £600, to change all the brake pads and disks, full service etc.
Interior trim is typical French build quality and will generally fall apart after a year or so. I.e. electric window panel pulling out of door.
If you buy a Megane new, make sure you sell it before the warranty runs out. If you buy one used, be prepared for it to fall apart.
**Update**
May 2008.
Previous problem was solved at a cost of £210, had an electrical unit changed out or something, forget what it was.
New problem, hydraulic clutch pipe has split and been leaking out clutch fluid all over driveway, clutch kept getting stuck depressed and made gear change difficult. Fixed at a cost of £130.
Car is now being washed and am planning to part exchange for a Fiat 500!