Bottom end packed in at 90k miles (oil pump).
The car eats drive shafts.
Feels like I'm constantly changing tyres.
Changed wishbones at 80k.
Various other sensors replaced.
Probably more, but can't think at the moment.
Superb performance and handling, super tight chassis, and loads of feel through the steering.
Unfortunately the car suffers typical Peugeot reliability issues.
Engine had to be replaced due to the oil pump giving way and taking the bottom end with it. The car had a full and up to date service history, and gave no warning.
I managed to evade the dreaded cambelt snap, which is all to common on these cars (see www.306gti6.com for loads of info). They need changing every 40k at the latest, and this will cost you £400.
Insurance is reasonable if you're a bit older (I'm 26 no NCB and pay £700 FC).
Fuel consumption is dreadful; 26-27MPG mixed driving.
All that said, if you get a good one, it will make you smile every time you get behind the wheel.
If you're viewing a GTI-6, there are a few things to look out for.
Listen for a loud ticking from the engine; evidence of cambelt snap that has not been properly fixed. Walk away.
Check the air con is working and is ice cold; the air con pipes on these are prone to rusting through (they are underneath the radiator), and these will cost £70 each to replace plus labour charges.
Make sure all electrics are working (lights, rain sensitive wipers, windows, mirrors etc), as electrics aren't a Peugeot strong point, and will cost a fortune to fix.
If you can afford the running costs and future repair/maintenance bills, I would recommend getting a GTI-6. For this sort of money, there is nothing else that can make you feel like a 306 GTI-6!