Does anybody use Akonadi, Nepomuk, Strigi, Soprano, Virtuoso ?

[joe at actionline.com]

Does anybody use Akonadi, Nepomuk, Strigi, Soprano, Virtuoso ?

What is the purpose and benefit of all this stuff?

Doing "locate akonadi" on my system found more than 200 files.

Is there any good reason not to get rid of any and/or all of this stuff?

I have read that they just eat up space and memory and cause one's system
to run slower.

Where can I find a list of other changes I could make to make my systems
less cluttered and more efficient?