We stay in, but we're never much for big crowds anyway. However, it's a big day of cooking, drinking, festive wear and games. Honestly, it's taken over as the biggest holiday in my family. Halloween is still number one for me, but they go all out.
I lived in Savannah during college. No one else does St. Patty's day bigger! Green fountains, green rivers, hotel rooms booked 2 years in advance, no open beverage laws, and thousands of people crammed into about half a square mile. No one walks. There are so many people, we all end up levitating a few inches off the ground and you just get shifted to a new destination.
A bit much for me, but if you're into that kind of party, Savannah is the place to go.