My $.02...
When I upgraded my mac mini to Lion I could still access my Snow Leopard SMB shares on my iMac but when I upgraded my iMac to Lion I could no longer access the SMB shares from the mini anymore in Boxee. Turns out Lion uses a new version of SMB that the current version of Boxee doesn't understand yet. As a workaround I just mounted the shares on my mini into a local directory, e.g:
mount -t smbfs //<username:<pwd>@<imac_IP>/<smb_share> /<local_dir>
like:
mount -t smbfs //user1

assword@192.168.1.1/share1 /local_mounts/movies1
then in boxee, I just add the local directory as a media source and boom...I'm back in business until Boxee adds support for this new version of SMB.