There was a study done several years back that determined that, if a given program took more than X seconds to respond to user input, it was considered "slow" regardless what was happening behind the scenes or how fast the program actually was. Because of this perception, calculation intensive programs like spreadsheets are so that the information that is currently displayed is recalc'd immediately. The rest of the spreadsheet (the part that is not currently displayed) is recalc'd as a background task. Similar gymnastics are done with indexing on interactive database programs, repagination in word processor, etc.
So, the program appears to be faster - and more responsive - than it actually is.
Just some food for thought.