This problem has been bugging me since the release of Mac OS X 10.6.

The fix seems to be quite simple, I added the following to my global block in smb.conf:

[global]
dos charset = UTF8
unix charset = UTF8
display charset = UTF8
unix extensions = no

Now we can work without errors again.

Ps. Don't forget to unmount and re-mount your share before the changes take effect.

Thanks for this info!
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I did a fresh install of Snow Leopard on my Macbook and soon realized my Samba shares were broken through finder - but still worked from the CLI.

Worse still once I tried to access the shares Finder would basically be dead, you'd need to Force Quit it to make it work again.

Eventually I reached for tcpdump and wireshark and found it's the pesky .DS_Store files again, seems my QNAP is denying access to them, Finder did not cope well with this.

A quick bit of hackery of my smb.conf solved it:

veto files = /.AppleDB/.AppleDouble/.AppleDesktop/.DS_Store/:2eDS_Store/Network Trash Folder/Temporary Items/TheVolumeSettingsFolder/.@__thumb/.@__desc/
delete veto files = yes

Once I got this removed and samba restarted my shares were working again in Snow Leopard. A bit annoying but not too hard in the end.