This text is in latest Skywards Newsletter:

Spread the word and refer ten of your friends and family members to join Skywards and collect up to 4,000 Miles the first time each friend flies on Emirates. Your friends can start enjoying Skywards benefits straight away, beginning with their first-flight bonus Miles. Please click below and log in by 31 March 2012 and we will send them an invitation to join on your behalf.

I do not know if it means you must refer ten people to qualify or if they really mean up to ten people.