You couldn't get anywhere near the size of Facebook on SQLite. Even a FogBugz or BaseCamp type of application on SQLite could be problematic if you are doing lots of writes.
The driver you use to connect to the database is also very important. If I'm not mistaken the PHP driver was pretty terrible a while back. It may be better now. It didn't handle the locks well which sometimes resulted in deadlocked queries with only a handful of users.
Personally, I wouldn't run any multiuser application doing a significant number of writes on SQLite except during early development. I think where it really shines is when you need a lightweight embedded SQL database without the hassle of having to install something extra. Think Amarok or something similar.
I ran Trac on SQLite for a while. Setup was a breeze and performance was reasonable with 3 or 4 users, but a switch to PostgreSQL was a night and day improvement.
If you're set on using an embedded database you might want to check out Firebird or H2. I haven't used Firebird myself, but I have had excellent results with H2. You have the flexibility to use it a few different ways - embedded vs. server mode and in-memory vs. disk storage - and it is very compatible with MySQL syntax so it's useful as a drop-in replacement.
The driver you use to connect to the database is also very important. If I'm not mistaken the PHP driver was pretty terrible a while back. It may be better now. It didn't handle the locks well which sometimes resulted in deadlocked queries with only a handful of users.
Personally, I wouldn't run any multiuser application doing a significant number of writes on SQLite except during early development. I think where it really shines is when you need a lightweight embedded SQL database without the hassle of having to install something extra. Think Amarok or something similar.
I ran Trac on SQLite for a while. Setup was a breeze and performance was reasonable with 3 or 4 users, but a switch to PostgreSQL was a night and day improvement.
If you're set on using an embedded database you might want to check out Firebird or H2. I haven't used Firebird myself, but I have had excellent results with H2. You have the flexibility to use it a few different ways - embedded vs. server mode and in-memory vs. disk storage - and it is very compatible with MySQL syntax so it's useful as a drop-in replacement.