The ff package is a great and efficient way of working with large datasets.
One of the main reasons why I prefer to use it above other packages that allow working with large datasets is that it is a complete set of tools.
When comparing it to the other open source 'bigdata' packages in R
- It is not...

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