In general MS SQL is supposed to be an install and forget product for its Express versions. However this is not quite tue. For instance: databases should be backed up on at minimium a daily basis. With the latest incarnation of SQL Express, which will store upto 10GB of data the preformance of larger installs is of greater concern. Ava have a significant number of installs where the database is in the 4GB - 10GB range. We constantly monitor for performance and will adjust the database so that performanace is not degraded when for one reason or another SQL automatically decides that there is a new and (sometimes but not always) better way to send information back to users. The following link has a list of (free) tools that can help IT departments to understand how SQL is working.
Also but not included in this list (when we last read it) is a utility for backing up SQL express databases, it is free if you use it for only two databases and not expensive for larger numbers: