OS X 10.9.3 Update causing coreservicesd lag
This is what fixed the problem for me:


Rebuild the Quicklook cache (in Terminal: qlmanage -r &amp;&amp; qlmanage -r cache)
Rebuild Spotlight index (sudo mdutil -E /)


I'm not exactly sure which one of those two really caused the problem. You can try them separately.
It takes a while to rebuild both the cache/index, but afterwards Finder worked as expected.