I've always been a fan of the referral program that Avast used recommendation tab. The only thing that disappointed me was that once you obtained it, there was no incentive to keep recommending more to the Avast software.
While I still recommend people to Avast, it would be nice if the incentive would reset after the free license expired allowing for the award once again for continued loyalty and recommendations.
Side note: I have no problems paying for this valuable software, in fact, when my free 3 year license finally expired I of course renewed with the paid subscription because it IS that valuable.