From the Readability Blog:
All users—free and paying—now get unlimited access to their Reading List, Favorites, Archives, and all our other features.
We’re currently decoupling application features and supporting publishers (and Readability). “Premium” is now becoming “Subscriber”, and the dollars you can now optionally pay are purely for supporting us and writers, rather than to avoid the pain of any software-imposed limits we previously had.
Direct to Readability