The expos are good for general info. I went to one in NY in 2005. It was good for getting your feet wet and just getting a taste of different stuff out there.
Keep in mind however it is basically a big sales convention for vendors. Even during the 'general' presentations, these are put on by vendors (usually) who at the end make a product pitch.
So, good for general stuff and meeting other traders, not so good if you are looking for exact trading methods and such. There were some courses you could pay for that I heard were much more in depth, but for my first one, I did not pay for any additional classes while there.