I've experienced the fairly common slow open and save dialog box issue that seemed to come about with Mavericks and stick right through Yosemite.
The following solution has worked temporarily for me:
1) In Terminal: rm ~/Library/Caches/CloudKit/CloudKitMetadata*;killall cloudd
2) In Activity Monitor: Force Quit cloudd
But the problem always returns. I wanted to share the above temporary solution, but also to see if anyone has come upon a permanent solution yet.