I've decided to try Picasa for organizing my photos. It's a client app somewhat similar to local Danbooru: it tags pictures, spots people faces, sorts photos by time, mass adds/deletes EXIF, geo-tags and so on. The photos itself are not changed and remain in their original locations and all the information is kept in the Picasa database. So far so good.
Problem is I have several picture sets which need sorting. One is photos, another is all sorts funny pictures. I don't like mixing those because it feels stupid when Edward Elric is with your classmates in your "People" list. Picasa lets you categorize picture folders into "Collections", but this doesn't solve everything and what if your second database is stored elsewhere? On the removable drive or LAN? Picasa has only one profile.
Internet mostly suggests ugly-ish solutions with special programs which switch Picasa database before starting the app, or tells you to keep a second database under a separate Windows account (it'll have its own). But it's so clumsy to relogin simply for accessing another collection.
And then suddenly someone have had a really nice idea. Create a separate Windows user, set up the database as required (incl. create a juniction from AppData\Google\Picasa to where the database is stored), and then login under the main user and run Picasa using RunAs.
Windows has this feature where it can run applications under a different user without leaving your session. Hold Shift and right-click the shortcut, then choose "Run as" from the popup menu and enter login and password. You can even make a special shortcut which will always run Picasa under a chosen user.
This is way easier than switching and maybe even better than if the database was chosen with a simple "Which database to load?" You can limit database access rights on a system level, and then give passwords to some and to others don't.