Because I'd seen reports to the effect that KDE runs faster as root, I set up KDE as root on a spare computer. Lo and behold, it starts faster and runs faster - not quite on par with KDE3, but closer.

This could just be an issue of process niceness or something, but somehow I don't think so. I've noticed that Akonadi fails to start, as mysqld doesn't like to run as root... Maybe Akonadi is more of a resource hog than it should be? Or could this be something else entirely?

Oh yeah, one other thing: I know full well that running the desktop as root is a bad idea. That's why I did it on a machine that has nothing important on it. For those not in the know - if you want to test this, then please, don't do so on any computer that requires some level of security.

It's easy enough to test if Akonadi is the reason why you feel your computer is slow. For a temporary test, you can use the dbus-based akonadictl to stop the akonadi server. For a more permanent fix, and more details, see the userbase page on akonadi.

I have an old 2005 laptop with the following specs—Pentium M 2 GHz, 2 GB ram, nvidia 6800 Go card (nouveau drivers) and twin monitors (1920x1200 laptop display and a spare 1680x1050). This comp doesn't use akonadi and doesn't use nepomuk. I believe I also don't use desktop effects there and the cummulative effect of this is that the computer uses about 230 MB of ram and is extremely nimble. Possibly not as fast as a kde3 install, but fast enough to give it a run for its money. And pretty, too.

By now, nepomuk and desktop effects are extremely well-behaved components and on any reasonably current machine, a joy to use. Akonadi will probably get there over a few more releases, but for now, it's just having growing troubles.