Every so often (this is today's theme ;) I hear someone say something along the lines of, "I don't need Nepomuk Desktop Search. All my files are properly arranged in a neat folder hierarchy. I am not in need of any help with that, so Nepomuk is a waste of resources and I don't care to have it installed."
I am sure that such people are right about one thing: they have their files highly organized in a great filing system that they use with a great degree efficiency, and as such don't need something to index those files for them.
Nepomuk, however, is not about indexing files, at least not exclusively. It is one things Nepomuk can help you with, but they call it a "social-semantic desktop project" and not a "index your files project" for a reason.
Nepomuk is being used more and more to track, coordinate / orchestrate and index non-"files on my disk" data. Let's take two examples: Akonadi and the Plasma Desktop.
Akonadi is using it to provide search for email, contacts, events, etc. which is one step away from the "file indexing" idea. Instead of building its own search database (and all the overhead that implies), Akonadi is able to lean on Nepomuk for that and, as a bonus, be able to not only index but map the correlations between those sets of data which, as a human being, we'd expect to be there and have at our fingertips.
The Plasma Desktop is going even further with Activities. We now have the ability to store, retrieve and mark as "active" which desktop activity you are working on. There is no file anywhere that maps to this. KWin will be gaining the ability to map windows to these activities, and any other application (KDE or not!) can also choose to map internal data and settings to activities and take appropriate action when the Activity context changes. The mechanism that ties this together? Nepomuk. Since we're using Nepomuk, we get the ability to tie documents and other URL based locations together with Activities as well .. for free.
For me, Nepouk's ability to index my files is a nice feature. It's also one I currently have turned off due to personal preference. Nepomuk's real feature comes in the form of all the indexing and, more importantly, correlation services it provides for all the more ephemeral data and workflow that happens on my computer. Right now Nepomuk is using less than 2MB of unshared memory on my laptop (yes, including the Akonadi bits). That's a fair price in my eyes for that functionality.
Critiquing Nepomuk as a file indexer is therefore selling it short and missing out on the real opportunities it represents. Those opportunities only grow as we exercise one of the attributes that KDE has long been known for: our ability to integrate technologies horizontally across our applications and libraries. The more we use Nepomuk for the things it was truly designed to make possible, the more we'll see the benefits beyond it being a file indexer.