Hi All
My Stilo is usually very good, although I have removed my passenger side door trim at the moment (new one coming soon), and the passenger side of the windscreen will mist up (temperature gradient is high).
I had a Brava 1.8 ELX w/out Air Con, and that had chronic mist inside it. Whatever you do, don't use those "Anti-Mist" repellants you can buy - all they do is smear the screen.
Athanasios, is your problem on the front windscreen, side windows, or back window. I know that, if i switch off my Air Con, it will start to mist at the bottom - my brother had a Peugeot 307 that used to cover the screen in mist when you turned the A/C off - apparantly it throws hot air up to kill any bacteria in the system, which'll also cause your screen to mist up.
One thing that helped my lovely Brava overcome this problem was clearing the outer air escape vent - it was located behind the bumper on the passenger side. It was caked in mud and stuck closed - when I unblocked it and opened it, a small amount of water came out, with loads of damp air. I then put some WD40 on it, and that REALLY helped reduce the misting. Check yours isn't blocked.
Stilo 1.6 Dynamic, 5dr, 2002, Crystal Green