Although I agree with Politicus that the fair representation principle is more important in the abstract, such principle can only fully prevail in "civilized" countries like the Scandinavians, where a hung parliament doesn't result in utter chaos.
You haven't been paying attention to Sweden much this past autumn I hear.
When it comes to electoral law it does seem that Italy has a preference for making things as complicated as possibly imaginable. Which of course is fun for us election geeks, but must be really confusing for the average voter. And it does inevitably seem that no matter which system you have the voters seem to hand you unstable situations anyway.
I do really think Politicus raises an important point. The political system forms the political conduct, not only for the voters but also for the politicians. The reason that things are (supposedly) more civilized in Scandinavia is because our system forces there to be broad coalitions, while politicians in Britain are incapable of compromise with the other party because they're used to either always having all the power.
I don't think this system will last. What happens for example if the Lega becomes second largest party at the next election? Southern right-wingers voting for the Lega in the run off? I do really think you guys would have been much better off by just keeping the old system and just neuter the Senate's power, alternatively reforming the senatorial electoral law.