Not really. It is almost instantaneous in all cases (except when the disk needs to spin up). I don't touch type, so I watch the keyboard as I type. When I look up at the screen everything has been found.
When I browse by artist or genre there is a short lag, but not more than 1 second from I click on the artist until the list is shown.
The library is on an external 250 GB Maxtor FireWire disk. The machine is a 17" PB.