How to fix OSX client to Windows share hangs?

Nope, Apple is replacing Samba in 10.7 because it's GPLv3. (And Apple is avoiding GPL like plague. See, they're also slowly moving away from GCC).

Now, to answer the original question, it seems like the connection is "simply" lost. And as the mounting is done at the kernel level, it can completly hang the machine.

I think your issue comes from a sudden loss of network connectivity. Here's what I would look for :

• A change of IP address (server or client) : maybe a DHCP lease is expiring ?
• Maybe some form of WiFi issue if you're over WiFi

This is probably a bug in samba, Apple is replacing it in 10.7 for just these reasons.

That being said I would assume your connection is dropping and not being re-created. Take a look at this post where users are having similar issues: https://superuser.com/questions/144327/mac-os-cant-connect-to-smb-shares-after-sleep