I used Mail ever since I switched to a Mac. I just love the simple and elegant look, it is much more convenient than any web app. However, since Lion I actually hate it a lot. The long-awaited third column is glitchy and cannot be properly customised. The conversation view does not work with most e-mail providers including, to my astonishment, Gmail, whereas the much more useful view by thread function is gone. Furthermore, the simplified e-mail header is an impairment; it shows not enough in compact mode and too much in extended mode, while the save-attachment button is only viewable in the extended mode. For me, Mail for Lion feels like an unfinished product and I would love to get the old version back.
I think that Sparrow becomes more and more a solid alternative to Mail. It has some refreshing ideas, like the Facebook and Dropbox integration which seem very useful to me. The interface is much cleaner and the overall structure of the program is much more simple. However, I cannot use it as it does not properly support my university and work e-mail accounts. It works well with iCloud, Gmail and Yahoo, but not very well with other accounts. Also, I think Sparrow offers not enough customisation options, e.g. to remove the pictures in the mail list and to view all your folders at once, not only the folders per account (at least the last time I used it).
