Forgive if my description is not very thorough, my coworker actually discovered this and I'm just reporting it through the grapevine since I figure it will help.
The issue is that Leopard would not connect (via "Connect to Server" in GUI) to Samba shares when none of the shares were browseable. In our smb.conf, we had set browseable = no in the global configuration, as well as browseable = no in every share's configuration. It was determined that setting a share to browseable = yes would allow Leopard to connect via GUI. In fact, setting ANY one share to browseable = yes would allow Leopard to connect via GUI to any share.
Around here, we don't make any shares browseable as it provides a little extra layer of security. To workaround this issue for now, we created a fake share with browseable = yes and everything works as expected.
Please let me know if there is any more useful information I can provide.
How is this a Samba bug? I'd call this a Leopard issue.
Closing out bug report.