It might be a minority opinion, but I'd rather there not be a referral system.
Here's why:

1. Skeptics already are using words like "scam" and "ponzi" to describe Steem, and many of these skeptics have large audiences. Having a referral system would just reinforce that opinion.
2. As internet marketers started spamming their referral links to their email lists and social media subscribers promising them money if they just signed up and then signed up their friends, user numbers would skyrocket. Value would inflate rapidly with it, forming a bubble. Then the vast majority of those users would never touch their accounts again, and the difference of "signed up users" vs "active users" would be a black mark against the site that the skeptics above would use to further criticize it. The bubble would pop, skeptics would have yet another knife to use, and the future of the site would be in question before it even had a chance to get really established.
3. Quality > Quantity.
   Currently there are good discussions. Get an influx of would-be marketers just looking to make referral money, and you'd have the Warrior Forums in article form. If people think all the articles about Steem itself are bad now (we've even got whales publicly announcing they'll no longer upvote those articles), they've seen nothing compared to what it will be like around here once the WF referral marketing crowd gets their hand on the site.

Just my $.02, for what it's worth.