Steam is more than just a place to buy PC games. It's also a forum for discussing them, rating them, and amassing the associated trading cards. There's a layer of social functionality, too, plus user-generated content and the ability to Greenlight auditioning titles. Valve restricts access to some of those features, though, and it just raised the bar for what it takes to become a full-fledged user.
The firm's "limited user" policy previously required accounts to make a purchase or accept a gift to gain access to the full slate of features. Now, you have to have spent at least $5 in the Steam store for full citzenship. Activating game codes doesn't count, but having funds in your Steam Wallet does. So does activating a pre-paid Steam Wallet card.
Valve says the change is meant to curb abuse, adding:
Malicious users often operate in the community on accounts which have not spent any money, reducing the individual risk of performing the actions they do. One of the best pieces of information we can compare between regular users and malicious users are their spending habits as typically the accounts being used have no investment in their longevity. Due to this being a common scenario we have decided to restrict certain community features until an account has met or exceeded $5.00 USD in Steam.
A fiver seems like a reasonable threshold for PC gamers, so it's hard to argue with the policy. After all, freeloaders can still use their accounts to play games—they just have to pay a cover charge to participate in the wider community. Thanks to Rock, Paper, Shotgun for the tip.