Echoing what Kirk said, it's always better, safer, and normally faster to ingest first then edit from the ingested files on the hard drive.
Also, after any OS X update there are 100s/1000s of new files on the hard disk that Spotlight needs to index, resulting in a temporary system slowdown until that indexing is completed - it could just be that, and you can tell if the spotlight indicator in the very top right of the screen has a pulsating dot in the middle.
Also, assuming your camera disks all have the same name, you could try adding them to the "do not index these disks" list of disks in the Spotlight pane of the system preferences.
Rgds,
Ben