A friend bought a new 21.5-in iMac for his wife. He wondered why it was slower than the 24-in 2008 iMac it replaced. It was taking MS Word 38 seconds to stop bouncing on the dock & actually start working. I suggested a few possibilities and eventually it was realised the poor thing was still indexing its content after having over 18,000 sizeable photos thrust at it from a back-up drive.
It's working fine now that the indexing is done.