com.apple.sidebarlists.plist
, had acquired several keys with very long values (all named Bookmark
); the lengths ranged from about 2.7 MB to 4.3 MB which made the size of the preference file larger than 11 MB. It appears that whenever an operation occurred that needed to access the (sequential) preference data from that file, reading the entire file brought everything to a near standstill until complete. (When I was looking at the file with an editor I experienced the same slowness in moving through the file.) Removing that file has eliminated nearly all the slowness that I was experiencing since switching to Yosemite and continues to do so.