After upgrading to Leopard, whenever I would try to mount SMB shares on my company's network, the Finder would hang interminably on the "Connecting to Server" progress dialog (the network is Active Directory-based).
My password, like many that of many people, contains some extended characters. Today I tried URI-escaping the password, and it worked! I was able to connect immediately to all shares. To URI escape a password, try the following:
ruby -ruri -e 'puts URI.escape("YourPasswordHere")'
Copy and paste the result in the Finder's username/password dialog, and mount away!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071030144902362