[srcmap]

What about this: Use SQLite.

Make it one SQLite file per user. All the read/write are parallelized per user. Backup db file would be smaller, easier. Each service node can handle N users, less for heavy follow users. Should be easier to scale horizontally the with user count by adding system nodes and Storage, networks, web handling process.

[freeplay]

Interesting concept but it falls apart pretty quickly once you start adding in the "social" parts of the network.

Also, you're still going to need to index all posts somewhere. Unless you don't want search functionality on your site.

[geysersam]

Interesting idea. However, how do you query things like "list the followers of this user"?

Edit: search also becomes difficult

[rich_sasha]

Where do you put cross-user events? Like retweets or likes?