This is my first time at OOPSLA (http://oopsla.acm.org). All the IT conferences I've been in my life have been Microsoft events, TechEd, MGB, etc.
The format of the OOPSLA is quite different. There are a few sessions for the whole attendees instead you must choose Tutorials, Panels, Posters, Onward… . The only general sessions are the keynotes, but this ones do not start until Tuesday.
The other big difference i'ts about food. All Microsoft events are full of different types of beverages and candies, and I prefer to not mention the food served at lunch. Here at oopsla there is only coffee but it's not in plastic glasses there are real cups !!, and today's food was really delicious.