These were devised as a way to keep the site ad free - we don't consider ads as they are on the modern Internet to be worth the bytes they take up. After a small focus group with some randomly selected users and some lengthy internal debate, we've decided that the easiest way forward is to add subscription tiers. Very important note: The addition of these will not, in any way, detract from the core experience of the site. That's something we've been committed to from day one. What these will do, however, is improve that experience by increasing a few limits.
Freshwater: Upload size limits are doubled, and you get a nifty profile badge.
Groundwater: As above, but 5x the upload size limit instead. Additionally, you'll have the option of viewing videos and listening to audio in original quality rather than the transcoded, bandwidth saving version. You also get beta access to new features in testing.
Springwater: The highest currently planned tier, intended for artists and those serious about supporting the site. On this tier, you get a 10x upload size limit increase, increased number of images in an imageset, and access to a massively more in depth blog analytics page than regular users will get, giving you breakdowns on how people are finding your posts, which posts were likely to have resulted in how many follows, and more - basically, close to the same dashboard the staff will be using for the site as a whole. In addition, you'll have the ability to promote a couple of your posts for seven days each month - these will then periodically show in a user's sidebar instead of the randomly selected featured post. The current ratio we're thinking about for featured:sponsored showing up is 70:30, just so that folks aren't inundated with sponsored posts. Note: This does not insert it as a regular post on a user's dashboard, and will only show to users who appear to be interested in the same stuff as you're drawing (after all, we figure you want folks who are gonna be interested in following to see your stuff). Additionally, you'll be able to make sale pages - things like one-off adoptables and brush packs (there may be a small fee taken on sales of these, but it will be negligible if so - you're already giving us money). This tier will be constantly iterated on based on feedback.