I noticed a few small changes this week that might have something to do with this - the history button was moved from the top right (up by Admin), over to the top of the folder section as a little binocular button. At the same time, the filter option that existed for the folder section has gone away...
I'm not seeing a slowdown in my searches, but maybe some additional changes were made re: history/filtering/searching? Can someone from Marketo add more info?