The first day at JSM is always a bit sluggish, as people slowly drip in and get their bearings. Similar to last year in Washington D.C., the meeting takes place in a huge conference centre and thus there is no feeling of overcrowded . It may also be that the peripheric and foreign location 

Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).