Where are network shares mounted in the filesystem?

[Chanchao]

When I add a network share folder in nautilus (Connect to server...)
then I get the icon for the new share on the desktop.

However, in file/folder selection dialogs these don't appear. 

Suppose I right-click a link to a file in Firefox and want to save it to
a network share..  How do you do that?  The shared folders don't appear,
but are they mounted somewhere in the filesystem so I can access the
place?

I checked /media and /mnt and so on but... nothing.

Cheers,
Chanchao