Hey, mine is supercharged right now... I've been meaning to make an up to date thread about it but haven't had time.
It's running at 0.2 bar boost, I think 0.3 bar is the most she'll do. Power response is really great, feels like the 2.0 litre they should have sold!!
The intercooler works amazingly, the supercharger is literally too hot to touch but past the intercooler it's back too air temperature. It's going on a rolling road in a couple of weeks, I'm hoping for around 30bhp above stock... I would not expect any more, but otherwise the engine is standard.
Turbo is the way to go if you want to really go crazy horsepower, but with the supercharger you don't need to change the fuel system... everything just works amazingly smoothly, it's free power.
Feel free to come and take a look... I'll be in Southampton on Saturday with another Alfa owner doing his cambelt.