In no particular order:

* The download speed advertised by your broadband provider
* The speed listed on your Wi-Fi kit
* The battery life quoted by hardware manufacturers
* The 4x speed increase if you move from a Powerbook to a MacBook Pro
* The 2x speed increase if you take an intel iMac over a G5 iMac
* The song capacity on any MP3-style player
* Leprechauns