We use Windows SharePoint Services (WSS) 3.0 and have several network drives that we map to various document libraries. While we can use the browser to navigate and retrieve documents, I find that using Explorer with mapped network drive letters is faster. It has also worked well for providing a seamless transition from our old network shares.
This week traversing folders and retrieving files using these mapped network drives came to a grinding halt. It would take 5-8 seconds each time I clicked to open the next folder. Opening a file took even longer.
Disabling Automatically detect settings within Internet Explorer (Tools > Internet Options > Connections > LAN Settings) did the trick. It worked this time too.