This is pretty interesting. I'm not sure I understand what you mean though about separating databases "by user". Could you elaborate on that? How would my application's database change if I were a user of this service?
Sure. Basically each user would have their own database file generated on account creation. Then in your app, instead of doing something like:
connectDB("/path/to/db")
you would do:
connectDB("/path/to/$user/db")
Also, if you needed to query all of your users data in aggregate, you would use the 'ATTACH' capability of SQLite to essentially create a master database. Note that you will need to design your scheme appropriately (thoughtful table/column naming, etc) for this to work well. See: http://www.sqlite.org/lang_attach.html
