This tip is not written down anywhere. Don’t you just hate that? I guess it will all come together sooner or later, but meanwhile, here is a tip for doing searches in Lion Mail.
Put the name of a person you are searching for in the search window in Mail. If you just put in a first or last name then you may get several options. If so, click on the one you want and it will appear in the search field next to the word “From”.
Click on the word “From” and you will see that you can choose between From, To, and Entire Message for your search — just like you could do in Snow Leopard.
Hope this helps.