searching, there's a site search feature, which admittedly I haven't used in a long time and I've heard it has become very arcane. There're also subscriptions, which I have used, it depends how consistently your database reports results (subject / title consistency).

If the designs of a number of .NSFs are the same, sure, you can move data docs among them with relative ease. It's even possible to take dbs from different servers and merge them together as replicas -- while this isn't supported and takes some clearing of replication times, it does work.

There are subtle issues even with identical .NSF designs. Anything your users assume because "it's in this database, and not that", clearly that information will not be preserved when the data is merged together. This can be aggravating. It may be useful to tag docs from each db so you can distinguish them: because if it becomes a factor, you'll be doing development to support each source db.

When the .NSF designs diverge though, then you're getting into development territory. Views may display (badly) the documents they don't expect to be in the db. Forms and other design elements may be named the same, and may stomp on one another.