With Sparrow 1.2, the email client gains connections with Facebook (for displaying friend pictures and adding friends from within Sparrow), a unified Inbox, support for Gravatar, Subject-based threading, the option to create a new message by Control-clicking Sparrow’s Dock icon, and localizations in eight languages. A variety of bugs have been fixed as well. I still can’t consider Sparrow as a usable Gmail client due to its newest-first conversation sorting (so threads must be read from the bottom up) and extremely slow load performance for message bodies. A free Sparrow Lite works with only a single Gmail account. ($9.99 via the Mac App Store, free update, 11.9 MB)
Compare More Easily in Apple Mail
In Apple Mail, if you need to work back and forth between two different views of Mail's mailbox contents, you can do so quite easily. For example, you might want to look at a mailbox holding all filtered-in sales orders from the past week while also looking at a smart mailbox showing unanswered customer questions.
To avoid constantly clicking between mailbox views and losing your context each time, choose File > New Viewer window to get a second window and then arrange each window as desired.