Network shares can't be ejected? ("Ghost" share problems)

Question

This topic is to try to solve a problem I'm having, as well as many of my Mac friends, when they use a network share, and it then cannot be unmounted.
Basically, there are servers no longer accessible, because we switched LANs, etc.
Symptoms: in the Finder, clicking on the "Eject" button next to the computer's name gives out a dialog telling "A disk on <share name> is in use. Try close applications. (approximately).
Of course, closing all applications doesn't have any effect, neither does relaunching the Finder.
In the Terminal, the command "mount" displays, among others:
//GUEST:@ines:139/Shared Docs em Vaio1 on /Volumes/Shared Docs em Vaio1 (smbfs, nodev, nosuid, mounted by xxx)
//GUEST@ines:139/Download on /Volumes/Download (smbfs, nodev, nosuid, mounted by xxx)
I tried umount "Shared Docs em Vaio1", as well as the other share, and yet it outputs "not currently mounted"
I then did lsof to check what files were open on these share, and the output starts with lsof: WARNING: can't stat() smbfs file system /Volumes/Shared Docs em Vaio1
Output information may be incomplete.
assuming "dev=2d000004" from mount table
lsof: WARNING: can't stat() smbfs file system /Volumes/Download
Output information may be incomplete.
assuming "dev=2d000005" from mount table
I've reached the end of my meager knowledge on this issue, which is minor (in the sense that performance is not affected), but relatively present nevertheless.
Of course it goes off when rebooting, but I want to be able to solve this problem without a reboot, so how can it be?

Answer 1

I don't know if it is the same with SMB shares, but with AFP ones I sometimes get this message when the share point is on my MacBook & it goes to sleep. The 'solution' -- such as it is -- is just to wait for the client Mac to notice the server isn't responding & pop up a server disconnect notice on the screen. Once you click the 'ok' button in that notice, the share point disappears from the Finder & no more messages about something on it being in use appear.
This notice can take several minutes to appear. I don't know of any way to speed up the process, or if it would be wise to try. I assume the long timeout is so that brief network outages are not problematic.