Lion has some changes in SMB. It breaks--that is, literally breaks, EMC Celerra if Celerra is not patched.
(The other issue we found is that it apparently breaks Cisco's VPN client, however the built in Lion VPN client will work--however, you can't use the encrypted password--though the password is pretty easy to decrypt anyway.)
I've forgotten if it changed behavior by sending a null packet or not sending. Regardless, the change managed to send our EMC into fallover mode.
Now, the other issue is that the kernel upgrades have broken cifs on the Linux end. (Whether it's in cifs utils or the kernel itself, I don't remember. As of kernel 2.6.40, you may have trouble mounting //server/whatever/whenever
However, mount //server/whatever works--it's when you get into multi layered paths that there's a problem. I've only see this on Fedora, as it has a 2.6.40 or higher kernel, and Arch, with the 3.x kernel.
I wonder if it's possible that you're running into that? The way to tell is try to mount a path that is no deeper than //server/share, as opposed to //server/share/subshare.