After updating to Mac OS X Lion you may have lost access to your My Book World's Samba shares.
This problem can be easily fixed by updating mDNSResponder's config file.
Edit /etc/mDNSResponder.conf. It contains a line that says:
"your hostname" _smb._tcp local. 139
Change it into
"your hostname" _smb._tcp local. 445
Save the file and restart mDNSResponder using this command
Now you should be able to connect to your Samba share's again.