It will introduce some latency, but if you can't move your app off this server why not move you database to a server that gives you space to work? Your db does /not/ have to be on the same box as your app these days ;).

On the otherhand, think of creative solutions around it - is your db size limited to 100mb, or is that your quota? Low volume sites can get by with sqlite, which is simply a local file in your home directory.

That said, I've never thought about how to manage distributed dbs. Assuming there is a single, centralized app using them, the problem is actually a pretty simple one since you really only have to maintain state knowledge at a single point. The trouble comes in when you want to start doing fancy relational things with the data, since you are in effect breaking the link among related tables that containing them in the same db provides.

A brute force solution would have you keeping only a single table (or part of a single table) on each db (provided they don't need more than 100mb each). This would render the "relational" part of the RDBMS mostly ineffective, unless you included small look up tables on each of these single table dbs (or had a single db for each look up table). In the end, trying to make things relational would force you to reimplement a lot of this functionality in your app (poorly).