I only use Lightroom for photo manipulation — I don't want or need the catalog feature. Nonetheless, Lightroom repeatedly pesters me with messages asking me to back the catalog up.
How do I disable these messages?
Lightroom always uses a catalog to store your edits, however you can disable the backup notifications.
Go to: Edit->Catalog Settings (PC) OR Lightroom->Catalog Settings (Mac)
Set: "Back up catalog" to "Never"
Edit->Preferences->General->Go to catalog settings->General->Backup->Never
The answers above are correct, but I'm not sure why one would want to disable this function. All the develop adjustments are stored in the catalog, so if the catalog file crashes you'd lose all your adjustments (other than any exported files you'd made, of course - but these wouldn't tell you what specific adjustments you'd done, they'd only give you a jpg or tif output from those adjustments). Having a regular (even if only monthly or so) backup of the catalog seems very useful to me, even if you never use the Library function.