It is pretty easy to get referrals to any program, you just simply promote your referral links. However earning commissions from those referrals can sometimes be a lot tougher than just promoting your link.
We all know that it is easy to advertise a Traffic Exchange inside another Traffic Exchange because the members already know what they are. Same with promoting Mailers inside other Mailers.
The thing is now that there are so many Traffic Exchanges and Mailers about that people cant upgrade in them all so the take up rate for upgrading from referrals found in other sites of the same kind can sometimes be fairly low.