Mentionning it as it disrupts work flow. Your mileage may vary.

Everytime I switch tab (change grids) or come back to IQ, there's a 1-2s delay. (Something like that goes on : first the grid gets the focus, then the tab gets the focus, then the toolbar changes color, and the formatting buttons change, etc. Everything happens in a slow succession and until everything is completed, nothing is possible)