Yes, Mac OS Lion will be getting a new Mail Client. It even gotten a new icon, which have a metallic looks. Overview of the Mail.app seems to be very very similar to what we have seen on iPad’s mail client. They want to have a more generic looks and feel so users will feel very familiar when they use mail on iPad and Macs.
Mail.app will have a conversation view for emails. Yes, same look and feel of iPad’s mail.