Hey there. That's a good question. every connecting computer has its own little database (you can find it in ´~/.ssb`), so you won't be downloading everything from every user ever. as you follow more people and post more things yourself you'll start growing your database, that's true. The solution for some people (using desktop clients) has been to remove old files from their blobs folder from time to time. the blobs folder is a collection of attachments and files that your computer requested from the network after receiving messages containing them.

Some others prefer lower hops counts. In Patchbay you can set the number of hops (explanation here). The default in most cases is 3.

I've been fairly active, follow a nice bunch of people and post regularly. Including cached content my database is currently 9gb. I have not ever wiped blobs or truncated things in any way. So I guess it's okay so far ;)