Hi,
I'm also seeing the issue of a disks, shares going away from the remote machine, but still on the server.
From my Win7 machine I would be happily connected and see files and then poof "File Not Found". If I connect from another machine say a XP box to same said files they are there.
I usually telnet on the tower and search for the smbd process for the win7 user and kill it. That then resolves the issue for another period of time.
There is nothing in the syslog that indicate anything untowards.
Looks like smbd is crapping out or getting it knickers in a twist for some reason. Can't remember when I started seeing this but it's happening on the latest few releases.
cheers.