I think it comes up quite a lot faster on my system since I switched from
the open source (but nasty) nv driver to the Nvidia closed driver and
enabled compositing.
I really don't see what it could be doing to be so much slower without
composite though :-( Maybe it's just that my system is less loaded since
the reboot ;-)
I like krunner but I too find that its usefulness as a quick access for
functionality has been impaired when it takes a long time to appear.