Network Drive won't unmount

Sounds kinda liek your iBook is lagging what way are you ejecting the network drives? Are you dragging them to the trash so that the Eject button appears? Try that if you are not doing that and see if you don't get as delayed a response.

-Internet Wiz

You can try using the Finder's Network -> server name -> "Connect..." button to show you what volume(s) your Mac thinks it is still connected to on the server. This should display a list of all its volumes you have access rights for, including any you are already connected to. The mounted ones will be greyed out, & there is no "disconnect" option for them, but it will at least tell you what the Finder thinks you are still connected to.

More of a workaround than a fix, but have you tried relauching Finder? (One way: Option-click on its Dock icon & choose "Relaunch" from the popup menu.)

This works for me when my list shows an icon-less volume or when the server quits responding & Finder is slow to notice that it has.