I participated in eRewards for some time. To join it you need an invitation from FB. The eRewards thing is about filling in opinion polls (about financial products, consumer goods, etc). For participating you get some points that you can later transform into FB miles.

I stopped participating because you get only very few points. It takes ages until you can earn enough for 500 miles. Also I found the questions pretty private and you often do not get the fuoll amount of points for a survey because they might not like your answers. Finally, if I remember it correctly, there are some restrictions about transforming your points into FB miles.

I still get their invitations for new opinion polls. But I ignore them. It is a waste of time.