If your iPod Nano or Classic is slow and seems to hesitate between switching around items, then you might need to update your firmware to version 1.0.1.

In this upgrade, there are fixes that seem to fix the sluggish response when switching between screens, and an unresponsive click wheel.

To get the latest update, plug your iPod into your computer, select the iPod in iTunes’ Source list, and click Check For Update in the Summary tab.

There is also a good review of this update available on the playlistmag.com site that shows a battery comparison chart for the classic, both before and after this upgrade.