We have multiple sites I'm working to migrate into Linode (basic LAMPs).

Since many of the sites basically use copies of the same tables (I.E. calendar, geography info, etc.) I'm considering making a standalone MySQL linode from which all the sites would pull. (reference library link) The non-specific info would be in one schema and the site-specific info would be parsed into their own schemas. Loading all the sites into a single upgraded linode isn't an option because we don't want them all crowding into a single IP.

The first obvious thing I see is requiring two db connections per site, for the main and site-specific DBs.

Is this a good idea, or am I just making more work in the long run?

This is generally the way to go, as long as you are ok assuming sysadmin duties to another box.

With the database separate, you can take advantage of multiple web servers to scale an app for instance.

There's no way to accurately answer that question without running real-world performance tests.

Without those tests, any answer you get would be no better then a coin toss.

Each website will have it's own characteristics and it's own traffic patterns. Depending on what those are, a standalone db might have better performance, it might not - the only way to KNOW is to test both scenarios.

In my OPINION (for my production boxes), a standalone DB is rarely worth the extra network traffic and system administration overhead unless you are maxing out the server in Web app usage alone, at which point I'd up the server specs instead of splitting the app servers - YMMV.

_________________
Either provide enough details for people to help, or sit back and listen to the crickets chirp.
Security thru obscurity is a myth - and really really annoying.