I've seen 2 games against Samp, Parma, both in the San Siro. Inter won both, 3-0 and 3-1 respectively with crowds of 60,000 for both. It felt f***ing great when Inter scored.
Unfortunately due to the difficulties of balancing college and work I haven't made it over to Milano for 2 years but I should make it late this year. Been saving the pennies.
I'd certainly recommend it to anyone, it really is a unique experience but obviously its gonna be difficult if your in the US or whatever. The San Siro is the best stadium I've been to (I've been to Old Trafford, Bernabeu and Nou Camp).
I'll always remember the universal horror in the stadium in 95/96 when it was announced that Festa would start against Parma. Those who seen him play will understand It was a pretty funny moment