I've been keeping an eye on Sparrow (Sparrow - The New Mail for Mac) and just shelled out my $10 for it on the Mac App Store. I have used Mailplane for years, but it's getting a bit bloated and long in the tooth, plus it now replicates Web capabilities. I like Sparrow because it is tiny and minimalist, but it lets me do all the stuff I do with Gmail (use the same keyboard shortcuts---notably, to archive, label, etc). When it gets down to it, I mostly DELETE e-mails. All I need to see is the subject (my credit card statement is ready; work needs an extra person next Tuesday; someone left a comment on my blog...). Sparrow lets me keep a Twitter for Mac--like single column that I can buzz through and just delete. Also, the threading is pretty. Did I mention the keyboard strokes I use work? Probably heavy e-mail users will want a heavy-duty client, but those of us seduced by the new iOS-looking apps will like Sparrow. Reportedly it will soon support services other than Gmail, but for now not so. They had a downloadable beta until this morning, but now you have to buy to try, sadly (GigaOm has a decent review with some screenshots).